Has anyone experienced this with their cleaner shrimp?

[dirtyxducks19]

I’ve had my cleaner shrimp for about 3 months. A couple of weeks ago I noticed a black spot on its side. Later I caught it picking at it. The spot disappeared after it molted but reappear a few days later. It’s on the shell/exoskeleton. It seems like a sore or would. I have an BTA. Could it be a sting? Should I worry about infection? Is there anything I can do to help?
Thank you!

 

[Anchor]

I have had this on a shrimp before. just not a cleaner.. it went away after several molts.. I recall someone somewhere on here mention it is a parasite or something just under the exoskeleton.. Still have that shrimp a year later.