As an additional point I need to add to the other thread. It is common to have pain in lower power workouts vs higher power workouts. This is because the higher power demands lead to more force in the legs that effectively lifts our bodies a bit and reduces the pressure on our sit bones.
So, “easy” rides often hurt more and/or sooner than “hard” rides. See the thread for suggestions to relieve the extra pressure.
I have the same problem on long rides. I only noticed the issue on 3+ hr rides. The solution for me is a saddle with more padding. Most saddles today unfortunately are minimalist, no padding. I’ve tried over half a dozen different saddles to try find something comfortable for long rides. The one consistent thing on the most comfortable is that they have more padding.