Update to uZEUS PWR Switch problems:-
Replaced switches in both uZEUS modules and inserted jumper in each.
All LEDs working correctly with no flicker etc.
Removed jumpers, everything still working correctly.
I have probably never used my Eurorack system more than 100 times, so any wear and tear on the switches could be ignored.
Therefore, I have to conclude that the problem IS caused by mechanical stress on the solder joints caused by the original threadless switches not being anchored to the Front Panel.
Will report in the future if anything changes.