@Gnant - I have noticed the same thing but I have always thought it was the “luck of the draw”. For instance, sometimes the hub does not actually go into inclusion mode even though the app says it is searching… I then try again using the old app and it works (this is true whichever app I use first I believe), or I reboot the hub and a previously undiscoverable device pops up immediately.
My suggestion is to visually check that the hub is indeed in inclusion mode either by looking at the LED on the front or looking at the Event List for the hub. Once confirmed then put the device in inclusion mode. If that fails, then try a reboot of the hub. After each attempt, I always do an exclusion and a reset of the device for good measure.