@CH71
The error moves with the CT.
See what happens with a (temporary spare) CT from your second VM3 you will get soon.
VM3 measurement problems were often discussed here and the cause were mostly not fully “clicked” clamps, wrong phase cable assignment or damaged clamps. (See the topics shown down this webpage. For example: Victron VM-3P75CT Energy - wrong power number - any idea? - #3 by Luc )
A very good picture of not fully clicked CT is here: VM-3P75CT Phase 3; it is not being measured correctly - #7 by ejfeith
A thick grid phase cable makes it hard to close the snap fully.