Here is an update:
TLDR: Switching o-rings and cleaning the reg fixed the problem.
When the original problem started it was caused by bad o-rings or poor o-ring matching. As such, switching back in the stock bolt fixed the problem.
After shooting a few more cases through the stock bolt I tried to re-tackle the problem by switching out all of the o-rings on the drive and bolt. this helped to an extent, but the consistency was really really bad.
Switching back to the stock bolt didn't help this time, so I cleaned and lubed the regulator and everything worked money after that.
Switching back in the goldbolt with the new orings and clean reg == it worked fine.