At first blush, the installed battery monitor might be faulty. Use a multimeter to test the battery with and without the battery disconnected. You can get an online chart of various state of charge voltages for the battery type. Battery should be tested “at rest”, after being disconnected from any charger for a while. Check its voltage with the charging operating, should be over 13.6 VDC.
I bought a budget shunt that came without connecting cable ;( Awaiting the cable from Amazon. My first LiFoPO4 battery has Bluetooth monitoring so I can check and by proxy, the second battery that is in parallel with the first.