Thank you for your assistance. Will try Escom and see how that goes.
I think the other guys figured this out. The Multi disconnects from the AC because the voltage goes too high (over 253V for more than 40 seconds). The loads on the input side are still there (they did not disconnect) and your Carlo Gavazzi is also still there sending data, which is why the overview may look a bit weird (non-critical loads are shown even though the grid is indicated as not available).
The utility is supposed to stay within 10% of the standard 230VAC. Which happens to be exactly 253V. Usually the fix for them is to change the tap on the transformer to a slightly lower one.
Then, just for completeness: It is actually possible to increase the voltage from your side by feeding in energy. I don’t think it is the case for you (because you are nowhere near the levels normally needed for this, and you said it also sometimes happens at night), but… Ohms law says V = IR. The electrical cable from the transformer to your house has resistance R. If you push current (I) from your side, V will actually increase. So in rare cases, with AC-coupled PV, I have seen disconnects based on overvoltage that was caused by too much PV and too thin a connection to the transformer…
But as I said, probably not the case for you. Your voltage seems to be above 240V pretty permanently… in my experience a good stable grid voltage is in the mid 230s. At my house it sometimes drops to around 226… it’s an old house, who knows what it was specced for… 
You can try switching to another grid code. For example “Other”. Other is not like None. It allows the ESS assistant to work, but doesn’t comply with any particular grid code.
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