Same here. I’m super tight in my hamstrings, glutes, and low back. Been that way for a long time so I have to be really careful when doing any lift that needs a flat back. Almost every time I get cocky and increase weight in these kinds of lifts I start to run into trouble. I’ve tweaked my low back more times then I care to admit doing this. I keep the weight low especially when doing high rep sets so I can focus entirely on technique. It takes a ton of concentration for me to stay in the right position and as soon as I start to fatigue the technique goes out the window.
I’d suggest keeping the weight very low if doing high reps and then on low rep/heavier days be very carful and don’t be afraid to pull the plug on the lift if your not confident in your technique.