12 week strength template question

Today during my squat warm ups my low back started to get stiff. It got worse with each set. I’m in the 3rd week of the 12 week strength template. My week 2 squats I went up to 530 at RPE 7.5 so I planned on working up to about 550@8. My last warm up was 495 and I could tell any heavier would be at least @9 so I stopped at 495. I was thinking that the volume on day 4 with the heavy block pulls and RDLs caused the stiffness in my back and effected my squats .Do you think I should lower the volume on day 4 or just continue and the stiffness will improve as I adapt to the volume?

I don’t think there’s anything in particular that is causing it per se’ and I do think overall that your recovery capacity will improve with more training. That said, main thing is to get the appropriate stress in for the day and it sounds like you did that.