I have tried and failed to reproduce the issue you, and others, have reported with adding the device in the new app. I have deleted one of my, admittedly older, double switches, reinstalled it and everything worked as expected. I can’t see anything in the code which would cause a different behaviour between older and newer switches in this regard.
I wonder whether it has something to do with the precise procedure used to add the device(s). If I go in the new app to the “room” labelled “No room assigned”, press the + at the top, then “add device”, then “Scan nearby” at the bottom. I then press one of the rockers for around 10 seconds. The scan reports that it can’t find the device, but when I go back to “No room assigned” , the devices are there, or appear fairly quickly. I see 2 devices with generic names in the app and the same 2 in the IDE. I then make the appropriate changes to the names, room, etc. either in the app or in the IDE.
I wonder whther there is some subtle difference in the way others do this, that might explain the behaviour they observe.