I had the same issue with one shutting down and sometimes watching a film it would just cut off completely. Both 28s are connected via a cable. Master to slave upon setup. Both 28s now have a separate feed each running to the harmony as we thought this may fix the issue. I have had the WiFi modem removed today by B&O and they fitted a commercial B&O access point which created a new WiFi connection.
This hasn’t resolved the issue. I really don’t know what else I can do. Any more suggestions?
My local B&O dealer have been here 4 times and still no luck.
Regarding changing WiFi from 2.4 to 5.2. I pick up my neighbours WiFi signal and today we removed my router for the B&O one.