There was a kernel bug (also reported on kde) a couple of years ago that was pretty much the same as this.

https://bugzilla.kernel.org/show_bug.cgi?id=204629

Thanks for this info. It is somewhat different from my situation, in that nothing is auto connected (and I can't find how to configure that), and manually connecting the device doesn't give audio too.

journalctl | grep bluetooth says

bluetoothd[1489]: profiles/audio/avdtp.c:avdtp_connect_cb() connect to 00:1B:66:BE:74:46: Host is down (112)
bluetoothd[1489]: src/profile.c:record_cb() Unable to get Hands-Free Voice gateway SDP record: Host is down

But if the Sennheiser is meant by "host¨, is is not down, it is in fact perfectly usable from my Android phone.

Maybe submit a bug again.

regards, Jogchum