Yeah, seems to be the same cause for me. Slow, grindy reps and the squat morning I get near limit loads.
It is blood pressure for sure. I can feel my face turning purple. I switched to Andy's HLM program for older lifers, and I did a 1x5 of solid squats today at 140kg without anything popping. Plan is to just stop if feel like the next rep will be a grinder.