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Check the small fuse holder, these sometimes get loose springs or oxidised or corroded contacts. While in there check all other connections. The fuse holder has been the cause of these problems in previous reports.
I checked the connections at the shunt and in the small red line fuse. I also checked the connection at the monitor. No joy, still reading 9.8v. Home bank still reading 13.2v.
I did remove a different Victron monitor from my other boat and tried it with this troublesome system. It reads the same 9.8v.
2 meters reading the same suggests you have another problem, where do you get the 13.2V from. Could you have another poor connection somewhere. Do you have a lithium battery with internal BMS, if so is this properly turned on. You could also try using the aux connection as another voltage sensor to check.
I get the 13.2v reading right on the house bank of Lithium batteries.
Yes, but details, multimeter on the battery terminals or Bluetooth from inside the battery. Multimeter from battery terminals really is the best because you could then check the voltage on the BMV aswell and see if you have voltage loss somewhere. A frayed wire inside the PVC covering of the voltage sense wire could also cause this if you used the same sense wire on both meters. Clutching at straws, and hard to diagnose over the net with limited info.
I got 13.2v using the multimeter on the terminals of the battery bank.
Is my shunt bad?
I have just reread one of your answers, you said you tried another monitor, I misread this, if use used the round display on the same shunt then it does suggest the shunt has partially failed, so contact your supplier. Final diagnosis is use a multimeter one lead on shunt body, one on the red wire at the shunt to rule out trouble in the sense wire.