@smoir in my experience with lichen planus - which I have had for several years but it was only diagnosed in recent years - I find eating any kinds of mushrooms triggers my condition, as does stress.

Perhaps you could try to avoid mushrooms (even mushroom gravy) to see if it makes a difference …? I get very annoyed at people who shrug and say, “just pick them off!” when something with mushrooms on it (e.g., pizza). They don’t realize that the food item is already “contaminated” by the mushrooms so simply picking them off does not work.