The Ready State Virtual Mobility Coach is like having a virtual Kelly Starrett in your pocket.
A couple of things to check. How is your shoulder IR/Hang archetype? If you watched yourself pullup, deadlift, push-up, swing etc, would there be a hinge/tissue fold in your neck. Do you grind your teeth?
Sounds like classic facet irritation. Everyone is flexion worried, but our athletic pops find way more grief with extension.