I don't think the inverter is the problem, because we can see there was no SOC wobble issue up until mid December 2023. The last update to the BMS was on 2023-11-30, but I can see the battery was holding charge in off-peak just fine on 2023-12-08.
In Mid December the WW variable charge rate feature was introduced. The battery was no longer able to meet the target, typically 3–6% short. I worked around this by overstating the battery capacity by up to 15%. I can see the SOC wobble is evident on December 26, when it completed a charge early.
I will try and set a timed charge via the GE portal and see what happens.