In a drawer we keep an ancient iPad 4 because of some software that can't run on newer iPad OS. Until today it didn't have the B&O app. Just today I downloaded the most recent version of B&O available for it: 3.16.1.38790.
Well, after logging it into my B&O account, the old iPad automagically downloaded my Deezer credentials and now only Deezer works... if started from the A6.
If Deezer is started from the BLC NL/ML, a warning is issued: "The selected product does not support playing Deezer content." However the BLC NL/ML can join the A6.
Baffling.