normally when these count down then back up they are trying to distribute uneven load,but i am sure there where some issues with the sensitivity of the board and there was a new board with a bigger tolerance for uneven loads.
The issue was with the mains transformer on the original board. This was changed – the way to tell if you have got the right one is – Old type of board has a red transformer on it, new one has yellow (when last I looked) one.