Thanks for the bug report! I’ve added this issue to our bug tracker, and it’ll be fixed in an upcoming release of FMOD Studio.
I’ve been able to verify that this issue doesn’t affect in-game behavior, so an instrument whose parameter conditions have been cleared will behave correctly in-game, even if it doesn’t audition correctly in FMOD Studio.
For now, you can work around the issue by deselecting and then re-selecting the event in the events browser after clearing the trigger conditions of an instrument or logic marker. This causes FMOD Studio to re-calculate all the event’s trigger conditions, resulting in their having the correct behavior.