Multiplus 2000 on boat trips when shore power is switched off

On my Victron intstallation on my powerboat of 3 Superpack batteries, Multiplus 2000 and solar, the AC from the Multiplus trips on and off in several seconds, bouncing in and out when I shut off shore power to leave dock, so becomes useless. Why?

please can you post some more information about your system, battery voltages etc?