I’m a Victron installer and install a lot of systems.
I have a system with x2 MultiPlus-II 48/3000/35-50 120V Inverter/ Chargers setup as a 120/240v split phase system set so it can charge with a 120v source. Typically it charges just fine with a 120v source but when the inverters have shut down due to a “Low Battery Alarm” they won’t start charging. I have replicated the system in our shop and it works the same way. I further tested it by then connecting a 240v source and then it starts charging them when the battery voltage is high enough it will continue charging using only 120v.
To allow 120v charging in the VE.Bus System Configurator under AC input I have unchecked switch as a group which will allow you to charge with 120v.
I believe this is a bug with this configuration or is there a setting that I can change somewhere else.