I suspect this could be an emotional response and there is nothing really wrong!
You have some solar
power so that should have kept the batteries up even with the fridge going and the inverter on.
What you are saying doesn't make much sense so please be more specific.
When the Victron was charging
at 50 amps how long did that last and at what voltage. Measured by what kind of voltmeter?
What do you mean by "the charger cuts out"? Does it go down to "Float" or do all the lights go out?
Can't get above 12.9 v. If the fridge is still on then what are you worried about?