With the Pebble Time smartwatch, the Fairphone 2 only works in a limited way: no WhatsApp messages, weather function deactivated. Do you know more about it?
I cannot answer the question conclusively. I don't use a smartwatch. However, I don't have any problems with WhatsApp or weather or Google Maps, etc. But I use both SIM cards (private and business) and it often happens that the SIM cards are locked and have to be unlocked again with the PIN. Possible explanation: Fairphone seems to want to prevent "bugging attacks". It is therefore possible that the Smartwatch is "recognised" by Fairphone as such an attack. But this is only a vague assumption. It is best to ask Fairphone itself.
I had the Fairphone for a short time, but unfortunately no longer. The software doesn't seem mature yet, it crashed quite often. Multitasking didn't work properly either. Too bad. I would have liked to support it.