F&F timer PCZ-522.3 retreats by one hour - how to stabilise?

Dear Forum Members.
I am having a problem with the F&F PCZ-522.3 timer that coordinates the duty cycle of the accumulation cooker.
It is a dual channel timer, with only 1 channel programmed, the other is set to the manual on/off option and remains off.

There was no problem with the configuration itself, everything set up so that the timer switches on the cooker on the cheaper electricity tariff.
The problem is that the clock goes back an hour several times a day. I've turned off the automatic summer/winter time change, set the time zone to UTC +1, and it still goes crazy. I've also tried configuration via NFC from my phone. When the clock on the device has switched I can send "current date" commands from the phone, to which it responds, unfortunately after a few hours it goes back again and so on up to several hours a day.

I don't know if this is a software fault or if I have misconfigured something.
I may be making a fool of myself, but is it possible to have "interference" in such a timer? The problem doesn't occur at the beginning and end of the heating season, when most neighbours are operating on a 'hold' basis and not heating their flats - then I have peace and quiet and my timer works ok.

Have any of you heard of a similar problem?
I am attaching a diagram of the settings.
Please do not hesitate to ask for help.
Little Kasia

I have a similar problem and this is with my second copy. After 3 months the system time was about 12 hours late I don't know what the problem is?