Hi Christian,
Can you try with the latest beta Venus OS beta firmware?
And please also test with gui-v1.
You asked for a ramping down the genset before stopping it: that exists, please check the settings related to the genset start/stop feature in your GX. Introduced here: Venus OS v3.00 - Generator warm-up, cool down and more - Victron Professional
Does require the genset to be started and stopped through the Gx (usually by means of a relay).