I made a video explaining the issue, but here is a step by step guide how to reproduce.
The issue occurs, when you change a Item Type on an existing rule, that has a sub-type selected. If the new items type has less sub types than the original item type the loot filters goes completely nuts and even other non-corrupted loot filters do not work anymore, until you restart the game.
Step-by-step guide how to reproduce:
Create a rule that has a Item Type condition with a sub type selected.
Change the Item Type into a new one, unselected the original item type, without changing anything on the sub-type.
It is really hard to explain in text form but I think the video should make it clear.
It is 100% reproduceable.
Here are my logs from those 2 sessions I recorded in the video:
Player.log (26.0 KB)
Player-prev.log (95.3 KB)