1st when does it flare up?
Then super long (but thorough) post:
For me personally it started with deads and mixed grip causing an un-level bar. It continued/carried over to Squats and butt wink. I am almost certain I am still fixing imbalances caused by mix grip and I haven't used it in I can't remember how long (easily 5+ months though).
I fixed deads by switching to hook grip. (I think every body should hook grip, aside from being even it also shortens the ROM a bit)
I fix butt wink through a long and continued process of staying mobile
Pause Squats with just enough weight to force me into position
I use the stretches after long layoffs to open me up a bit so that I can use the pause squats as a weighted stretch. Then I do my normal squats. I am currently stretching every day before all of my workouts. Record every rep from your 4 or 5 oclock to make sure your butt is not winking. Not wearing black helps to see as well.
I also use Pause front squats as a stretch as well.
My entire Squat workout goes like this:
Pause Front Squat 2s @ 135-225
Pause Pack Squat 2s @ 135-225 (Supersetted with Fronts)
Same Set Pause Squat 2 and Normal Squat 1 with 315
Normal Squat Rep and Set Progression
IGNORE THE WEIGHTS just treat those like 20%-30%-40% of 1RM.
My stretch list...unfortunately I don't know the real names:
Warrior Lunge (this is actual name and hits hip flexors)
Head to Toe (same position of warrior lunge but I lean way forward putting the stretch into my hips and hamstrings)
Frog Stretch (hip opener also real name)
Close stance toe touch (hamstrings)
Wide Stance toe touch (hamstrings)
Shoulder Dislocations (I use a PVC pipe and also rotate between putting it into a high bar and low bar position)
Don't train your hip flexors- most people when training abs are actually training their flexors which are going to make them tight and cause anterior pelvic tilt which will cause back pain by itself.
Don't under estimate upper back tightness helping to stop butt wink. 1 piece collapses and it is much easier for the rest to collapse.