I have the same issue, looks like after upgade to 2.5.10 and the new AVM binding, Dect 200 will not be supported anymore. I uninstall and install the binding again, no result. I delete one of my dect 200 things, no result, Every time I clean the caache so that could also not the reason. I have no clue anymore. In the OH Log there are no entries. Fritzbox itself is online.
P.S. I remember that the last what I done was to add a new Fritz200 Poweradapter - thats works. After the next reboot the Bindung can’t work with Fritz200.
P.P.S. Figured out for all who still run into the same issue. I disable one of the DECT200 Poweradapter in Paper-UI. In the result, the other things are going in offline - undefined - connection error.
From my point this is a bug. It must be possible to deactive a thing from the same type without result to other things.