Dave, power would be my first guess. I'd do the following:
1) Remove and insert the wire ferrel that goes from the positive side of the battery into the shunt, sometimes they don't seat right.
2) Check your batteries aren't dead using a volt meter, also check the voltage using one probe on positive side of battery and negative probe one each end of shunt.
3) Check the continuity between the positive wire from your battery to the shunt.
4) Grab an off the shelf phone cable (make sure all 6 conductors are wired up) and try that.
There's a also a trouble shooting section in the manual -
https://www.victronenergy.com/upload...S-SE-PT-IT.pdf