Multiphase regulation unstable

DIY
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1

I have 3 MP II 5000 in a 3 phase install. For 6 months no issues. From today the multiphase regulation is jumping up and down with 1kW.

pic1
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This is from the p1 meter. Did a reset on the 3P75CT to see if there was an issue.
Anyone a clue where to look ?

2

Try to check that all battery and mains connections are secure and tight, particularly battery negatives and Mins neutrals.