Using the latest release of EMF and ETF + Fabric 0.16.14, I get several related warns and errors upon startup.

[15:04:38] [Render thread/WARN]: [EMF]: no part found for: [mushrooms.visible] in [bogged2.jem]. Available parts were: {EMF_mushroom3, head:headwear, left_arm:EMF_left_arm#, body:EMF_body, root, EMF_mushroom2, head:headwear:EMF_headwear##, EMF_right_arm, EMF_bone, head:EMF_head, EMF_headwear####, body, EMF_mushroom1, EMF_right_arm#, right_leg:EMF_right_leg#, EMF_right_leg#, head:headwear:EMF_headwear###, EMF_mushroom2_2, head:headwear:EMF_headwear, EMF_left_leg, head:headwear:EMF_headwear:EMF_mushroom3, head, EMF_bone2, EMF_left_arm, EMF_headwear##, head:headwear:EMF_headwear:EMF_mushroom2:EMF_mushroom2_2, left_leg:EMF_left_leg#, right_arm:EMF_right_arm#, head:headwear:EMF_headwear:EMF_mushroom3:EMF_mushroom3_2, head:headwear:EMF_headwear#, head:headwear:EMF_headwear####, EMF_headwear#, left_arm:EMF_left_arm, head:headwear:EMF_headwear:EMF_mushroom1, EMF_head, head:headwear:EMF_headwear:EMF_bone2, head:headwear:EMF_headwear:EMF_mushroom1:EMF_mushroom1_2, head:headwear:EMF_headwear:EMF_mushroom2, EMF_body#, right_leg:EMF_right_leg, EMF_body, EMF_headwear###, left_arm, EMF_right_leg, right_arm:EMF_right_arm, head:EMF_head:EMF_Created_by_FreshLX_for_Fresh_Animations, body:EMF_body#, EMF_mushroom3_2, left_leg, left_leg:EMF_left_leg, EMF_left_leg#, head:headwear:EMF_headwear:EMF_bone, EMF_left_arm#, EMF_headwear, EMF_Created_by_FreshLX_for_Fresh_Animations, EMF_mushroom1_2, right_arm, right_leg, headwear} [15:04:38] [Render thread/ERROR]: [EMF]: Variable [mushrooms.visible] not found in animation [mushroom1.visible] of model [bogged2.jem]. EMF will treat the variable as zero. [15:04:38] [Render thread/WARN]: [EMF]: no part found for: [mushrooms.visible] in [bogged2.jem]. Available parts were: {EMF_mushroom3, head:headwear, left_arm:EMF_left_arm#, body:EMF_body, root, EMF_mushroom2, head:headwear:EMF_headwear##, EMF_right_arm, EMF_bone, head:EMF_head, EMF_headwear####, body, EMF_mushroom1, EMF_right_arm#, right_leg:EMF_right_leg#, EMF_right_leg#, head:headwear:EMF_headwear###, EMF_mushroom2_2, head:headwear:EMF_headwear, EMF_left_leg, head:headwear:EMF_headwear:EMF_mushroom3, head, EMF_bone2, EMF_left_arm, EMF_headwear##, head:headwear:EMF_headwear:EMF_mushroom2:EMF_mushroom2_2, left_leg:EMF_left_leg#, right_arm:EMF_right_arm#, head:headwear:EMF_headwear:EMF_mushroom3:EMF_mushroom3_2, head:headwear:EMF_headwear#, head:headwear:EMF_headwear####, EMF_headwear#, left_arm:EMF_left_arm, head:headwear:EMF_headwear:EMF_mushroom1, EMF_head, head:headwear:EMF_headwear:EMF_bone2, head:headwear:EMF_headwear:EMF_mushroom1:EMF_mushroom1_2, head:headwear:EMF_headwear:EMF_mushroom2, EMF_body#, right_leg:EMF_right_leg, EMF_body, EMF_headwear###, left_arm, EMF_right_leg, right_arm:EMF_right_arm, head:EMF_head:EMF_Created_by_FreshLX_for_Fresh_Animations, body:EMF_body#, EMF_mushroom3_2, left_leg, left_leg:EMF_left_leg, EMF_left_leg#, head:headwear:EMF_headwear:EMF_bone, EMF_left_arm#, EMF_headwear, EMF_Created_by_FreshLX_for_Fresh_Animations, EMF_mushroom1_2, right_arm, right_leg, headwear} [15:04:38] [Render thread/ERROR]: [EMF]: Variable [mushrooms.visible] not found in animation [mushroom2.visible] of model [bogged2.jem]. EMF will treat the variable as zero. [15:04:38] [Render thread/WARN]: [EMF]: no part found for: [mushrooms.visible] in [bogged2.jem]. Available parts were: {EMF_mushroom3, head:headwear, left_arm:EMF_left_arm#, body:EMF_body, root, EMF_mushroom2, head:headwear:EMF_headwear##, EMF_right_arm, EMF_bone, head:EMF_head, EMF_headwear####, body, EMF_mushroom1, EMF_right_arm#, right_leg:EMF_right_leg#, EMF_right_leg#, head:headwear:EMF_headwear###, EMF_mushroom2_2, head:headwear:EMF_headwear, EMF_left_leg, head:headwear:EMF_headwear:EMF_mushroom3, head, EMF_bone2, EMF_left_arm, EMF_headwear##, head:headwear:EMF_headwear:EMF_mushroom2:EMF_mushroom2_2, left_leg:EMF_left_leg#, right_arm:EMF_right_arm#, head:headwear:EMF_headwear:EMF_mushroom3:EMF_mushroom3_2, head:headwear:EMF_headwear#, head:headwear:EMF_headwear####, EMF_headwear#, left_arm:EMF_left_arm, head:headwear:EMF_headwear:EMF_mushroom1, EMF_head, head:headwear:EMF_headwear:EMF_bone2, head:headwear:EMF_headwear:EMF_mushroom1:EMF_mushroom1_2, head:headwear:EMF_headwear:EMF_mushroom2, EMF_body#, right_leg:EMF_right_leg, EMF_body, EMF_headwear###, left_arm, EMF_right_leg, right_arm:EMF_right_arm, head:EMF_head:EMF_Created_by_FreshLX_for_Fresh_Animations, body:EMF_body#, EMF_mushroom3_2, left_leg, left_leg:EMF_left_leg, EMF_left_leg#, head:headwear:EMF_headwear:EMF_bone, EMF_left_arm#, EMF_headwear, EMF_Created_by_FreshLX_for_Fresh_Animations, EMF_mushroom1_2, right_arm, right_leg, headwear} [15:04:38] [Render thread/ERROR]: [EMF]: Variable [mushrooms.visible] not found in animation [mushroom3.visible] of model [bogged2.jem]. EMF will treat the variable as zero. [15:04:38] [Render thread/WARN]: [EMF]: no part found for: [mushrooms.visible] in [bogged2.jem]. Available parts were: {EMF_mushroom3, head:headwear, left_arm:EMF_left_arm#, body:EMF_body, root, EMF_mushroom2, head:headwear:EMF_headwear##, EMF_right_arm, EMF_bone, head:EMF_head, EMF_headwear####, body, EMF_mushroom1, EMF_right_arm#, right_leg:EMF_right_leg#, EMF_right_leg#, head:headwear:EMF_headwear###, EMF_mushroom2_2, head:headwear:EMF_headwear, EMF_left_leg, head:headwear:EMF_headwear:EMF_mushroom3, head, EMF_bone2, EMF_left_arm, EMF_headwear##, head:headwear:EMF_headwear:EMF_mushroom2:EMF_mushroom2_2, left_leg:EMF_left_leg#, right_arm:EMF_right_arm#, head:headwear:EMF_headwear:EMF_mushroom3:EMF_mushroom3_2, head:headwear:EMF_headwear#, head:headwear:EMF_headwear####, EMF_headwear#, left_arm:EMF_left_arm, head:headwear:EMF_headwear:EMF_mushroom1, EMF_head, head:headwear:EMF_headwear:EMF_bone2, head:headwear:EMF_headwear:EMF_mushroom1:EMF_mushroom1_2, head:headwear:EMF_headwear:EMF_mushroom2, EMF_body#, right_leg:EMF_right_leg, EMF_body, EMF_headwear###, left_arm, EMF_right_leg, right_arm:EMF_right_arm, head:EMF_head:EMF_Created_by_FreshLX_for_Fresh_Animations, body:EMF_body#, EMF_mushroom3_2, left_leg, left_leg:EMF_left_leg, EMF_left_leg#, head:headwear:EMF_headwear:EMF_bone, EMF_left_arm#, EMF_headwear, EMF_Created_by_FreshLX_for_Fresh_Animations, EMF_mushroom1_2, right_arm, right_leg, headwear} [15:04:38] [Render thread/ERROR]: [EMF]: Variable [mushrooms.visible] not found in animation [mushroom1.visible] of model [bogged2.jem]. EMF will treat the variable as zero. [15:04:38] [Render thread/WARN]: [EMF]: no part found for: [mushrooms.visible] in [bogged2.jem]. Available parts were: {EMF_mushroom3, head:headwear, left_arm:EMF_left_arm#, body:EMF_body, root, EMF_mushroom2, head:headwear:EMF_headwear##, EMF_right_arm, EMF_bone, head:EMF_head, EMF_headwear####, body, EMF_mushroom1, EMF_right_arm#, right_leg:EMF_right_leg#, EMF_right_leg#, head:headwear:EMF_headwear###, EMF_mushroom2_2, head:headwear:EMF_headwear, EMF_left_leg, head:headwear:EMF_headwear:EMF_mushroom3, head, EMF_bone2, EMF_left_arm, EMF_headwear##, head:headwear:EMF_headwear:EMF_mushroom2:EMF_mushroom2_2, left_leg:EMF_left_leg#, right_arm:EMF_right_arm#, head:headwear:EMF_headwear:EMF_mushroom3:EMF_mushroom3_2, head:headwear:EMF_headwear#, head:headwear:EMF_headwear####, EMF_headwear#, left_arm:EMF_left_arm, head:headwear:EMF_headwear:EMF_mushroom1, EMF_head, head:headwear:EMF_headwear:EMF_bone2, head:headwear:EMF_headwear:EMF_mushroom1:EMF_mushroom1_2, head:headwear:EMF_headwear:EMF_mushroom2, EMF_body#, right_leg:EMF_right_leg, EMF_body, EMF_headwear###, left_arm, EMF_right_leg, right_arm:EMF_right_arm, head:EMF_head:EMF_Created_by_FreshLX_for_Fresh_Animations, body:EMF_body#, EMF_mushroom3_2, left_leg, left_leg:EMF_left_leg, EMF_left_leg#, head:headwear:EMF_headwear:EMF_bone, EMF_left_arm#, EMF_headwear, EMF_Created_by_FreshLX_for_Fresh_Animations, EMF_mushroom1_2, right_arm, right_leg, headwear} [15:04:38] [Render thread/ERROR]: [EMF]: Variable [mushrooms.visible] not found in animation [mushroom2.visible] of model [bogged2.jem]. EMF will treat the variable as zero. [15:04:38] [Render thread/WARN]: [EMF]: no part found for: [mushrooms.visible] in [bogged2.jem]. Available parts were: {EMF_mushroom3, head:headwear, left_arm:EMF_left_arm#, body:EMF_body, root, EMF_mushroom2, head:headwear:EMF_headwear##, EMF_right_arm, EMF_bone, head:EMF_head, EMF_headwear####, body, EMF_mushroom1, EMF_right_arm#, right_leg:EMF_right_leg#, EMF_right_leg#, head:headwear:EMF_headwear###, EMF_mushroom2_2, head:headwear:EMF_headwear, EMF_left_leg, head:headwear:EMF_headwear:EMF_mushroom3, head, EMF_bone2, EMF_left_arm, EMF_headwear##, head:headwear:EMF_headwear:EMF_mushroom2:EMF_mushroom2_2, left_leg:EMF_left_leg#, right_arm:EMF_right_arm#, head:headwear:EMF_headwear:EMF_mushroom3:EMF_mushroom3_2, head:headwear:EMF_headwear#, head:headwear:EMF_headwear####, EMF_headwear#, left_arm:EMF_left_arm, head:headwear:EMF_headwear:EMF_mushroom1, EMF_head, head:headwear:EMF_headwear:EMF_bone2, head:headwear:EMF_headwear:EMF_mushroom1:EMF_mushroom1_2, head:headwear:EMF_headwear:EMF_mushroom2, EMF_body#, right_leg:EMF_right_leg, EMF_body, EMF_headwear###, left_arm, EMF_right_leg, right_arm:EMF_right_arm, head:EMF_head:EMF_Created_by_FreshLX_for_Fresh_Animations, body:EMF_body#, EMF_mushroom3_2, left_leg, left_leg:EMF_left_leg, EMF_left_leg#, head:headwear:EMF_headwear:EMF_bone, EMF_left_arm#, EMF_headwear, EMF_Created_by_FreshLX_for_Fresh_Animations, EMF_mushroom1_2, right_arm, right_leg, headwear} [15:04:38] [Render thread/ERROR]: [EMF]: Variable [mushrooms.visible] not found in animation [mushroom3.visible] of model [bogged2.jem]. EMF will treat the variable as zero.

Further down the log there's this too, which may be related:
[21:03:30] [Render thread/WARN]: [EMF]: null properties found for: minecraft:optifine/cem/stray.properties [21:03:30] [Render thread/WARN]: [EMF]: null properties found for: minecraft:optifine/cem/stray.properties [21:03:30] [Render thread/WARN]: [EMF]: null properties found for: minecraft:optifine/cem/bogged.properties [21:03:30] [Render thread/WARN]: [EMF]: null properties found for: minecraft:optifine/cem/bogged.properties [21:03:30] [Render thread/WARN]: [EMF]: null properties found for: minecraft:optifine/cem/wither_skeleton.properties [21:03:30] [Render thread/WARN]: [EMF]: null properties found for: minecraft:optifine/cem/wither_skeleton.properties
The above section of the log was printed multiple times at different points.

do the custom models for the bogged work in game?

these are not always critical warnings