Take care that your battery is a 16S battery (51.2V) and the usual Pylontech is a 15S battery (48V).
So, if you set the voltages as per Victron guide for Pylontechs, those voltages are too low for a 16S battery like yours, hence the low voltage alarms.
Usually you need to set them about 56.5V bulk/absorption and about 55.5V float.
Of course, depends a lot on your BMS settings, especially the balancing minimum voltage, therefore set the float a little bit above that.