Manufacturers creating broken examples is sadly not unheard of. LoRaWAN and the air allocations on which it depends are more restrictive than many imagine, no small number of people have through lack of checking assumed they can do things which formally or legally speaking, they must not.
So I reconnected the Browan IAQ device at a greater distance (i.e. > 5 m, brick wall in between) and the join happened in a similar way as before. After that I don’t see any recent activity anymore on the ttn application page (i.e. no uplink message received in > 1h).
You should look in the gateway traffic page rather than the application page, to see if there is any activity at all.
Better yet, you should look for debug output (serial, etc) from the node itself.
The benefit of a “canned” node firmware is that it’s supposed to work.
The detriment of a “canned” node firmware is that when it doesn’t work, it may not be clear where to start debug.