How to verify control unit is still functional

My system starts with a very basic problem: the main control unit is behaving strangely. Tested various USB power supplies, reset the WLan config a couple of times, tested various locations. For the moment I can say it seems to work with a specific power supply in a specific location (where it cannot stay longterm). Nonetheless it has lost connection to all other modules. The other room modules show at least in the web interface as having been connected in the past, whereas rain and wind are missing there too. 

Long story short: how do I start to properly debug the situation?

BTW: the simple approach of replacing the control unit does not seem to work either, as it is not avaible without a lot of other stuff, that I do not need at this time.