It could just be the extra riding volume. I do some pretty long rides with 5-9 hours in the saddle. While I don’t generally have issues down there I find that discomfort can happen quite suddenly once you go beyond your normal riding time. For example if I’ve been doing only 1-2 hour rides for a while and then suddenly throw in a 6 hour ride I may get pretty uncomfortable beyond the 3rd hour and end up with a pretty sore ass by the end. It always amazes me how your body conditions itself precisely to whatever stress you are putting it through, but with little margin beyond!