The 890PX drive uses 10Pin CAT5 Patch Ethernet Cables to connect the CM module to each of the CD (phases) and CS (supply). Not an 8pin cable that may be more common. The CAT5 standard does not specify the number of conductors in a given cable. In the manual this is specified as "10-Way":
Among many things the additional pins are used for properly detecting modules (handshaking) as well as additional diagnostic information for current and voltage levels.
If you use an 8pin cable during a troubleshooting endeavor, it is likely to outright fail to detect a module: U V W MISSING PHASE.
However if you accidentally use an 8pin cable and it does detect a module you will still see odd faults such as Mx CURRENT BALANCE or UNDERVOLTAGE faults even if physically you are measuring proper current + DC Bus Voltage. This is going to be most common on the Uphase if it does not have the proper 10pin cable (it 'connects' but errors will be occurring); this is because an UNDERVOLTAGE fault is detected by checking the U Phase for bus voltage, and the drive first creates a check on the Uphase for for current balance.
Ensure that all three phases have 10pin patch cables if CURRENT BALANCE, UNDERVOLTAGE, or other power faults are occurring.