I might have another issue, though I want to do a few more tests before submitting it to bugtracker... perhaps anyone here has a similar experience?

When I woke up this morning, I tested Mitakuuluu by sending a message from my PC. It didn't arrive. In my PC Whatsapp, the "last seen" time was somewhere around 3:40am. (I had gone to bed around 9pm yesterday, Jolla was on the charger.)
The Jolla worked normal, internet connection was fine. Mitakuuluu claimed to be "logged in". When I sent message from Mitakuuluu to my PC, it didn't arrive.
Solution was to manually disconnect and re-connect Mitakuuluu, after that everything was fine again.

Could it be deep-sleep-related? Does the phone go into deep sleep while on the charger?
Edit: Apparently not: "Device doesn't go to suspend state if you keep it on usb cable"