question

I don't have a direct answer, but I see/hear my UPS's switching when the Victron equipment does its "transfer". All my computer/critical stations have a UPS to handle these situations... apparently they switch faster than the Victron does.

@OliSol

Possibly a brownout happening before the outage. You could experiment with tightening up on the V and Hz parameters to catch the failure earlier. There's a UPS function too, which will give the fastest transfer time. This pic is from a Victron article which suggests loosening them when a genset comes on in an inverting situation, but you seem to need the opposite..

The inverter isn't a true UPS, because it syncs to the grid it will track the grid voltage and frequency.

We have numerous failures per day, and the switchover is sufficiently quick to not restart sensitive gear (apart from LED lights that have a brief flick).

On very rare occasions, a device has restarted, that has been down to a grid brownout.

You may also see it if the batteries are a bit underspecced and can't handle the transient on cutover, though usually you would see all the power evaporate in this scenario.