Cause: The loot.filter file is not being parsed.
Fix: Inside mods\LFS\LFS.mpq\data\global\ui\layouts, ensure _profilehd.json has the line "lootFilterEnabled": true. Also, press Ctrl + F in-game to toggle the filter on/off (a notification should appear).
If your mod isn't working (game crashes, stash is standard size, or filters not applying), follow these troubleshooting steps: diablo 2 resurrected lfs mod offline fix for v exclusive
Assuming you have a mod package (like a "V Exclusive" drop mod or spreadsheet mod): Cause: The loot