Bug Report
First I used the VRM portal- Device List - "Firmware Update" update process to update my MulitPlus II from v496 to v497 which was reported as successful.
I next connected directly to the MulitPlus II and used the updated version of Windows Victron Connect, which failed to recognise v497 and requested to update to v497. I let the process continue and after the Victron Connect v497 update was happy.
So for some reason, the Windows version of Victron Connect failed to recognise the VRM v497 update or the VRM v497 was different.
At each stage, the inverter needed to be reset which means a short power interruption which the backup system is tasked with eliminating.
Thankfully v497 has fixed the Low Voltage alarm and now the MulitPlus will charge at the full 70A.