A short update:
- The battery voltage has been down adjusted to absorption 54.5V and float 54V. Many thanks for Cluj Napoca, Victron dealer for great support.
- The Fronius frequency shift values adjusted in ESS Assistant to: 51.00 / 53.10 / 53.20, after reading this post
Up to now it has tested OK during grid removal and restore, though with a 50% SoC battery.
Will do more test after reaching 100% SoC and still PV production.