Slave battery not reporting correctly

It appears that suddenly the slave 9.5 battery connected to an AC3 is not reporting its SOC correctly. It only charges to 50% overnight whereas the master charges correctly. I have also lost all correct reporting of voltages in GivTCP for that battery. I do have automations to charge the battery when off peak, and to export any excess at night, and one to shut off the charge power during the day to ensure the solar is exported in the summer, but nothing has changed with these to correlate. I am on 3015 as later FW versions caused major issues. Any ideas?

Update: have kicked off a calibration just to see if that alleviates the issue.

Al E.Gator It may help reduce the difference. A 50% discrepancy is a lot but it is normal for multiple battery setups to have differences in reported SOC. I have two batteries and it is normal for mine to have the primary at 100% and the secondary at 90%. If they are calibrated it will get to 100% or near enough after calibration but it soon (a couple of days or so) drifts back to 10% difference when the primary is fully charged.