Hello. OptiFabric and OptiFine modules both load as far as I can tell (by looking at the mods list in-game, plus seeing the "OptiFine_1.16.5_HD_U_G7" in the lower-left), but whenever I try to load any custom shader packs (SEUS, Continnuum), I get a bunch of missing textures and the whole game looks weird. Like either no textures load or otherwise I just get solid colors on all the blocks.

In my Resource Packs, Selected, I have Default on the bottom, Fabric Mods above, and I've tried with NAPP_2.0_free.zip or without, but the result is the same.

Any idea why I get all these "[OptiFine] File not found: textures/block/brown_stained_glass_pane.png" type messages?

[23/02/2021 21:00:26 PM] [main/INFO]: [OptiFine] *** Reloading textures ***
[23/02/2021 21:00:26 PM] [main/INFO]: [OptiFine] Resource packs: Fabric Mods, NAPP_2.0_free.zip
[23/02/2021 21:00:26 PM] [main/INFO]: [OptiFine] EmissiveTextures: Loading optifine/emissive.properties
[23/02/2021 21:00:27 PM] [21:00:27] [Worker-Main-26/INFO]: [OptiFine] Multitexture: false
[23/02/2021 21:00:27 PM] [21:00:27] [Worker-Main-12/INFO]: [OptiFine] Multitexture: false
[23/02/2021 21:00:27 PM] [21:00:27] [Worker-Main-22/INFO]: [OptiFine] Multitexture: false
[23/02/2021 21:00:30 PM] [21:00:30] [Worker-Main-22/INFO]: [OptiFine] Scaled non power of 2: fallingleaves:particle/falling_leaf_conifer_3, 5 -> 10
[23/02/2021 21:00:30 PM] [21:00:30] [Worker-Main-22/INFO]: [OptiFine] Scaled non power of 2: fallingleaves:particle/falling_leaf_conifer_2, 5 -> 10
[23/02/2021 21:00:30 PM] [21:00:30] [Worker-Main-22/INFO]: [OptiFine] Scaled non power of 2: fallingleaves:particle/falling_leaf_conifer_1, 5 -> 10
[23/02/2021 21:00:30 PM] [21:00:30] [Worker-Main-22/INFO]: [OptiFine] Scaled non power of 2: fallingleaves:particle/falling_leaf_5, 5 -> 10
[23/02/2021 21:00:30 PM] [21:00:30] [Worker-Main-22/INFO]: [OptiFine] Scaled non power of 2: fallingleaves:particle/falling_leaf_4, 5 -> 10
[23/02/2021 21:00:30 PM] [21:00:30] [Worker-Main-22/INFO]: [OptiFine] Scaled non power of 2: fallingleaves:particle/falling_leaf_3, 5 -> 10
[23/02/2021 21:00:30 PM] [21:00:30] [Worker-Main-22/INFO]: [OptiFine] Scaled non power of 2: fallingleaves:particle/falling_leaf_2, 5 -> 10
[23/02/2021 21:00:30 PM] [21:00:30] [Worker-Main-22/INFO]: [OptiFine] Scaled non power of 2: fallingleaves:particle/falling_leaf_1, 5 -> 10
[23/02/2021 21:01:13 PM] [21:01:13] [Worker-Main-23/WARN]: [OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@2e2b7996
[23/02/2021 21:01:13 PM] [21:01:13] [Worker-Main-23/WARN]: [OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@2e2b7996
[23/02/2021 21:01:13 PM] [21:01:13] [Worker-Main-23/WARN]: [OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@2e2b7996
[23/02/2021 21:01:13 PM] [21:01:13] [Worker-Main-23/WARN]: [OptiFine] Unknown resource pack type: net.fabricmc.fabric.impl.resource.loader.FabricModResourcePack@2e2b7996
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] Multitexture: false
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/andesite/andesite.properties
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/black/black_stained_glass.properties
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/WARN]: [OptiFine] File not found: textures/block/black_stained_glass_pane.png
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/blue/blue_stained_glass.properties
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/WARN]: [OptiFine] File not found: textures/block/blue_stained_glass_pane.png
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/brown/brown_stained_glass.properties
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/WARN]: [OptiFine] File not found: textures/block/brown_stained_glass_pane.png
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/coal_ore/coal_ore.properties
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/cyan/cyan_stained_glass.properties
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/WARN]: [OptiFine] File not found: textures/block/cyan_stained_glass_pane.png
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/diamond_ore/diamond_ore.properties
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/diorite/diorite.properties
[23/02/2021 21:01:15 PM] [21:01:15] [Worker-Main-23/INFO]: [OptiFine] ConnectedTextures: optifine/ctm/emerald_ore/emerald_ore.properties

Do you get this using just OptiFine with vanilla too? It sounds like something is unhappy where assets are being loaded from.