Devices on visible in dashboard

Hi. I have some devices that are for some reason not visible in device list in dashboard. As a result devices can’t be authorized. When I change network into open device can communicate without issues (using IP addresses assigned by RFC4193 addressing scheme - these are available even before devices are authorized) , but they are still not visible in device list. This has been first noticed today. Does anybody know what could be the cause? I don’t see anything wrong on device side.