Mysterious problem with the oven and the microwave

I would find that suspicious.

Apart from the fact that these three devices on a triple socket represent an extremely questionable constellation, I would measure the voltage... on the other hand, I would always bet in such cases that the refrigerator, due to its usually rather limited power consumption (with us usually only 220-240 volts), would be the first to stop working...

... very dubious...

Definitely check the sockets. It could also be that the neutral conductor is partially burnt and that's why the devices behave so strangely.