PWM Charge symbol flashing

I have 2 BlueSolar PWM Charge Controllers 12v/20amp connected to 2 x 200amphour Lithium ion BMS 12 volt batteries connected in parallel. The Charge controllers individually charged by 2 x 12 volt panels connected in parallel.
The system works well until the batteries are fully charged at which stage the Charge symbol arrow starts to flash at 2 flashes per second. I presume this indicates a Float state, although surprisingly and irritatingly there is nothing about this in the instruction manual.
Overnight the batteries power fridges so that they are about 80% capacity in the mornings. However the charge symbol arrows remain flashing and the current flow from the panels stays zero or very low. I then need to reset the controllers by re-entering the battery type (B4).
Why is this happening? It was never a problem with cheaper charge controllers which reverted to absorption charge automatically as soon as the battery capacity dropped.
Thank you. Ian