Do you have the RVU box?
If so, set it up to capture the fault 10 or 9. If you can capture the fault, you'll see a lot of other information occurring at that moment such as gate switch, door locks, BK and limits. If no data trap, it's process of elimination.
Also, I'd be checking the DPP tape guides for wear side to side and front to back. Does it only happen at the bottom? Maybe blipping the interlock?
If the drive is not faulting or even showing a warning, it's most likely not the HPV Drive.