...running the TV by itself not connected to anything else and with the DVD player and AV units turned off? What was the result? Did you repeat the experiment with just the DVD player connected? What was the result? Did you try experiment 2 with the DVD player powered directly from the mains, not in the surge protector? What was the result? Did you try experiments 2 & 3 with the AV units?

If you still get the problem with the TV alone in the surge protector, it would be one of those two. I'm not sure how stable the French electricity supply is (not very from your comments) but could the surge protector be responding to a spike from the line voltage and doing its thing to protect the attached equipment?

What sort of voltage converter do you have, a transformer (good) or a switcher (not so good)? Could feedback from it be triggering the surge protector? I vaguely recall some years ago someone telling me that running voltage converters through a UPS wasn't a good idea but I can't remember why and don't know if that also applies to surge protectors.

Incidentally, I have an LG TV, not OLED, and occasionally, it will just switch to standby - never comes back on by itself. I think it's a stray radio signal it's picking up because it does respond to the remote application on my LG mobile phone. Oddly, always about the same time on a Tuesday evening!