I have similar problems with 1 of the 3 EM's I have.
That one I frequently have to reset and reconnect to the WIFI AP.
I also have an 3EM. All 4 are next to each other on a din rail.
2 (1 EM and 3EM) of them have 3% package loss. An other one is at 30% loss and the problematic one is at 50%.
I don't see it can be related to the AP, because them all (or least the 3EM's) should have the same issue.
All 4 are on the latest firmware as of yesterday.
I would like to see an answer from Shelly on this. Maybe explaining why you changing the cables helping your situation can be explained.