GENERIC_PACK_STRIP_DIRS is not working

[amigthea]

Describe the problem

I got a .zip modpack where the folder structure is /modpack folder name/mods folder but when I load the zip with

      - GENERIC_PACK=/modpacks/modpack.zip
      - GENERIC_PACK_STRIP_DIRS=1

the server starts creating the game data but the mods folder is empty. If I repeat the process manually editing out the modpack folder name from the zip leaving the mods folder and the other files directly in to the zip root it works

Container definition

Paste run command or compose file here

minecraft:
[...]
environment:
- MAX_MEMORY=8G
- EULA=TRUE
- ENABLE_RCON=false
- MAX_PLAYERS=8
- OPS=redacted
- VIEW_DISTANCE=15
- ALLOW_FLIGHT=true
- MAX_TICK_TIME=-1
- TYPE=FABRIC
- VERSION=1.18.1
- GENERIC_PACK=modpack.zip
- GENERIC_PACK_STRIP_DIRS=1
volumes:
- ./containers/games/minecraft/data:/data
- ./containers/games/minecraft/modpacks:/modpacks:ro
[...]

Container logs

Paste logs here