Help with toadstool leather

[Omz]

Hi I am new to forums and not sure if I put this in the right place.
My toadstool started to develop what looks like rot and holes are appearing filled with rotting brown tissue. I upped the flow of my pumps in case it was detritus settling and causing the rot but more have appeared since so don't think this is the issue. There is no sign of parasites and none of my other toadstools are suffering the same issue.
Perimeters are all in check.
Question is should I frag it now to save what is left or would this heal after time as I have never had this issue before.
This is the best image I could get of the coral.
Thanks for your help.

 

[aznflyfisherman]

I think if it is rotting, it would be best to frag it into a couple pieces n hope the frags will regrow.

 

[Oly66]

Something could be nibbling on it like a hermit crab

 

[Uncle99]

When you say water parameters in check do you mean
76-78
1.025 SG
8-9 Alk
1320 mag
0 nitrate
0 phosphate
Looks like bad water rot