Right, so I've literally taken it right back to basics as you suggested disconnected all drivers except from the one. I was still having a weird issues where it would go into error state as soon as it was powered up, so I went back to the original 5Vdc PSU to power the drive rather than the 12Vdc and that solved that issue. Then I reset the firmware back to factory encase I had done something stupid along the way with the settings.

Then I connected the motor and the 130Vdc supply to the drive, and as soon as I hit the E-stop reset to power it up the motor continuously rotates until it reaches the max error in the settings.

At the moment I'm thinking either encoder is faulty (but all 3 do the same thing) or damaged drivers?

The only other thing I can think of that's different from previously is that I extended the encoder cables. I have double and triple checked the wiring is correct and swapping A and B has no effect. I extended it using CAT 5e cable, could this be causing some interference/noise giving a bad signal back to the drive?

I used shielded cable but the twisted pairs weren't shielded between each other, just the outside of the cable...

I also clipped the cable to the outside of the conduit supply the power to the motors, would this cause an issue?