Dear hadgraft and WeatherCat troubleshooters,
I have only recently purchased the Netatmo and it has been doing it from the start.
Unfortunately, no other WeatherCat users of Netatmo station have responded to my question. However, checking the WeatherCat release notes, the Netatmo station has been supported since February 2016. It is quite surprising that this sort of problem would not have been noticed sometime in the past 6 years. So it seems unlikely to be a flaw in WeatherCat itself.
Could you tell us what your configuration settings are for WeatherCat? In particular, on page 84 of the current WeatherCat manual it recommends (and I quote:)
The suggested sampling rate in WeatherCat is 10 minutes, non adaptive as this is the polling rate to the Netatmo servers (Preferences->Misc 2).
I'm not sure what the effect would be of configuring WeatherCat differently, but that is a possible cause for your problem.
Another less likely cause would be an issue with the station itself. "Rebooting it" would seems like a prudent action to consider. Certainly, I would check the owners manual for any troubleshooting tips.
Let us know what you discover.
Edouard