It has a problem with this textures :

in modern weapons content pack :

• Leopard 2A6

in WW2 content pack :

• STG 44
• FG 42
• Luger
• Panzerschreck
• SU-1-12

for all of that, it miss textures.

Fixed these for the next version.
See: https://github.com/FlansMods/FlansMod/releases/tag/v5.6-beta.1