Help with HBS507 drives!!

So basically I have a bunch of nema34 servo/hybrid drive/motors, all work faultlessly.. for some reason, anything smaller and it’s a complete nightmare ! So I was wiring up a box with some nema 34 drives (2Hss86a) no (well some) problem.. now the HBS507 was causing me all kind of jip.. moving erratically / noisily , not at all, alarms etc.. finally got it to a stage where it locks up under power but as SOON as i jog it, stall. I’m getting the 7 blip, position following error .. triple check all wiring , all seemingly good, continuity everywhere etc.. got to the point where I’m Losing my mind so change it out for the same motor / drive arrangement that was spare and 100% working the last time I used it.. IMMEDIATELY I get the same , locks up, moves smoothly but as soon as it moves more than about 30 rpm bam, same position following error and stall.. I’ve checked everything. I KNOW the wiring is correct because it was definitely working (I use the motors for motion control / camera stuff) and the motor in question, the second nema24/HBS507 came off a slider that I used on a shoot with no issue.. how is it possible that two brand new drives could develop a fault ? How is it that it can lock up, jog smoothly but not get to any speed without the alarm tripping ? The PSU is MORe than strong enough (36v / 41amp Dc) I’m at a stage where I’ve ordered yet another new drive and motor knowing full well these ones are fully working (at least I think they are) or have I unknowingly bought fake ones that only last for 5 mins before spontaneously dying ? If anyone knows what’s happening or has experienced something similar and overcome it I’ll love you forever if you can help me get to the bottom of it! Thanks in advance to any responders x