Why did the power cut have this effect?

I have two domestic Miele ovens, each with a clock.

Recently there was a power cut for about 30 seconds. One clock reset and the other continued as normal?

Why?!

I expect they have batteries in to maintain the time during power outages.
One of them probably has a dead battery. (Some use capacitors to keep
time but that will only work for a very short outage.)
Do you remember if they both used to keep time in power outages ?

Aha - that sounds jolly helpful!

I haven’t had a recent power outage…

If only an oscillator needs to be powered, an appropriately-rated “hold up” capacitor can easily keep it powered for many minutes.

Yeah. Sounds like there should be battery backup, so it’s likely that either one predates that feature or its battery has given up the proverbial ghost.

Very short YouTube video on the subject

And even if they’re the exact same model, it’s not at all implausible that the capacitor might have randomly failed in one but not the other. Capacitors do that sometimes, and a cap whose only job is to keep the time intact through a brief power outage isn’t going to be expected to hold to high quality standards.

Neither had I, then 2 in the last couple of months, several hours each.
The whole country is going to the dogs I tell you ! I blame tr%mp.