Deye hybride 8kW: power dip (40V) during transfer from grid to battery.

Lamp Relay switches off due to 40V power loss.
UPS load is 870W, battery is fully charged, grid voltage 237V.
Available solar power on MPPT 120W and micro inverter 39W.
Grid consumption (due to firmware bug) is 60W on display (realtime 0,7A)
50.8 is battery voltage. Grid cut off relay is set when V is lower than 50,6V.
When grid is cut off, lamp goes out (see drawing) and is some seconds later reactivated by a push button switch.
200V is measured inverter output voltage during switch over.
Is that normal?