Thank you all for suggestions and sorry for my late reply.
I have set archive_interval to 300 (was set to 120), but that did not improve anything.
Running weewx directly is confusing, because it not all sensor data is shown every time.
Anyway, it’s looks certain that weewx upgrade has not caused my woes. Actually, I was able to trace back "Temp outdoor sensor fault” message occurring regularly, just not for such large and noticeable periods of time.
But now I am getting a lot of failues, like today I had the message “weewx[7384]: wmr200: MainThread: W Temp outdoor sensor fault” logged 600 times. And I did replace batteries, too.
The only reason I can think of is unfortunate station location so that it is unable to receive outdoor sensor data.
Thanks and regards,
Ivars