OK, without the dimmer, it is less clear. However I'm reminded of the odd effects when the earth fails on car rear lights,

(rusty old Fords with more body filler than steel were prone to this...) and wondering if there is a continuity neutral problem.


Switch mode LED driver modules are often a "negative-resitance" load - that is to give constant light  over a wide voltage range, the electronics is arranged to draw more current at lower voltages to compensate, and with that type, if somehow you put 2 in series the system is unstable.

Unless perfectly balanced with equal voltage and current,, the one with less voltage will try to draw more current, so lowering its equivalent resistance, so lowering the fraction of the total voltage across it repeating the spiral,  until it goes out altogether and restarts.

Could it be that ?


But I cannot see how you would end up with 2 in series across the mains without a wiring fault of some kind, and I struggle to see how that could occur after you left. Unless it was just balanced by luck.

Mike.

OK, without the dimmer, it is less clear. However I'm reminded of the odd effects when the earth fails on car rear lights,

(rusty old Fords with more body filler than steel were prone to this...) and wondering if there is a continuity neutral problem.


Switch mode LED driver modules are often a "negative-resitance" load - that is to give constant light  over a wide voltage range, the electronics is arranged to draw more current at lower voltages to compensate, and with that type, if somehow you put 2 in series the system is unstable.

Unless perfectly balanced with equal voltage and current,, the one with less voltage will try to draw more current, so lowering its equivalent resistance, so lowering the fraction of the total voltage across it repeating the spiral,  until it goes out altogether and restarts.

Could it be that ?


But I cannot see how you would end up with 2 in series across the mains without a wiring fault of some kind, and I struggle to see how that could occur after you left. Unless it was just balanced by luck.

Mike.