Hey! I actually had this problem recently! In June, I updated a WHOLE BUNCH of comic pages that were marked mature and YES, it absolutely affected my stats for the month. It was a difference of hundreds of subs and now that I'm posting non-mature marked pages, wow, my sub count has suddenly recovered, HMMM. But yeah, Tapas kind of has to do that stuff since from my understanding their arms are twisted quite a bit by app stores.
Also, the page you link that was marked as mature er, isn't that mature? I don't think you need to mark it as M in it's current state. (The other update where she's washing herself should def keep the filter though!)
My advice is just to keep updating. Don't worry too much about the marked M pages, just move on and keep updating and those new updates will draw new folks in.