Mine shed their slime coat, the first time I saw it( I was new to cats) I wigged out but then after doin a lot of reading I read that it can be normal. My water parameters are always on point, I do a lot of changes and maintenance, but mine still shed their slime coats from time to time. What I have noticed in my own experience is that they tend to shed it when I do water changes and move a lot of stuff around in the tank (a little bit of stress), and, the main one I see is that it is followed by a growth spurt. I am not sure if growth can trigger it but my hybrid shed is a few times during a three week period where he grew over 4 inches, and my RTC just shed his the other day and today when I measured him, he was almost an inch longer than 5 days ago.
Im not saying thats what it is, I am just sharing my experiences. Like "thebiggerthebetter" said, bad water will stress a cat out and cause them to shed. If your water is on point and your cat isnt bein bullied by an aggressor, I wouldnt stress too much over it, just monitor him. Doin a big water change will prob cause him to shed some more just because the temp changes to fluctuate if you dont match your tank temp to new water and its a lot of activity. Keep us posted and let us know how things are going. Def check that water though, I check mine daily (some say its overkill but I am a fish nerd through and through haha).