Toadstool white patch no polyps??

[JWGarber]

I've got a neon green mushroom leather thats been in tank for 3-4 months. Went through one waxy shed about a week ago and looked really good. Polyps are always out unless prepping for a shed.

Today there is a patch of white that has no polyps doesn't even appear to be dimples where polyps would be.

I took photos but had picked him up to inspect so he is retracted.

Top corner near fold you can see there is a white patch that looks smooth.

Any idea what could do this? I did target feed some mysis and brine the other day. I fed the anemones and figured why not squirt some on the leather too.

Params from memory the other day...
CA 500
Alk 10
Mg 1600
PH 0
Nitrates are 25 or 50 dosing vinegar to bring them down
Haven't tested nitrites or ammonia in ages. Salifert kit is hard to read between the two colors.

Everyone else in tank seems good.

Just a side thought, what if my cleaner shrimp ripped then up trying to get a piece of food off him?? Would those polyps regrow or will that spot just stay bald?

Also he is swollen there. That top portion used to be a continuous piece not lumpy like it is now.

 

[JWGarber]

All polyps are extended like normal except that spot and it's getting bigger. Now it has doubled in size.

Is this just the start of it prepping for another shed? I've never seen it prepping for shed. I've always caught it fully closed then waxed over.