After playing around a while with the device I realized two things:
- I think if the device thinks there is a problem with the WiFi connection, it reboots
- Also the device seems unable to roam to a different Access Point
I saw that the AP it was connected to had a high channel usage, so I moved the AP to a less crowded channel and now the Shelly Motion stays on the network as it seems.
Can anyone from Shelly bring light into the behavior of the Shelly Motion regarding WiFi reception? Does it reboot when it's bad? Is it able to roam?