PeterG

Hi, you can find the specs for the shoto batteries here (make sure of the model number): https://www.solarwaysuppliers.co.za/wp-content/uploads/2021/07/Shoto-Residential-Battery-V131.pdf
 
My suspicion is that with a nominal voltage of 48V and a setting to start charging at 52V is what is causing the issue, as well as the discharge voltage of 42V is TOO LOW, the specs say 45V for the 48-100.
I would suggest changing the settings to start charging at 47-48V, your cut-off voltage to 45-46V and the end voltage of 54V (at 100% SOC) is correct and go from there. You may have been over discharging the battery with such a low cut-off voltage (3V below the spec).

Ok Ill try and help.
 
 
1 - You did select LI battery on the inverter ?
2. the error is the battery is not communicating, had the same when I had no battery, with the inverter. Did you use a custom cable as described in the manual ? its not the standard battery cable (LAN) cable that comes with your battery.
I got  a luxpower with Hubble had a cable made up, pluggen in and no issue - on my hubble i run SOC and Voltage as Hubble is adamant on the 44V battry cutoff, this cant be set to SOC only. 
 
3. Discharge setting must not be VOLT - off the top of my head there is a setting SOC BETTER i BELIEVE FOR THE li bms. THIS WILL ONLY WORK IF THE INVERTER AND BATTERY COMMUNICATE, just make sure your settings are as recommended by your battery manual.
Your settings look fine to be set up as a UPS, i think try get the battery to communicate with the inverter, then test. 
 

Id guess having two string if there is a failure in one string you still have the second string to help out if its one string then you loose it all. I dont think either way is an issue.