Size limitations for a WPA2 PSK?

    I've got a new Shelly 1 and want to integrate it into my existing network. Access point is a Mikrotik device serving three SSIDs and I can only connect to one of them with the Shelly. The only difference I can see is that the SSID it likes uses a short ("human friendly") 8 character PSK where as the other SSIDs use a longer 16 character PSK. That should normally not make a difference, but I'm running out of ideas what could have gone wrong. Does anyone know of such a limitation or have a different idea for how to debug it?

    I also experienced some problems connecting the shellies to the WIFI-Network. I had an easy to remember password with around 36 or 37 characters (with special characters) and that didn't worked with the shellies (and other devices). I then changed to a shorter one (but still longer than 8 characters) and without special caracters for that part of the network.