I cannot get Case 1 or 2 to work, but reading the above I did have location on my master set to "only when using app" so that might be the trick. I will try later.
I can get Case 3 to work. I've played around with plenty of ROMs on my slave and I am having the opposite experience from what Emil posed in his recommendation. Much more stable experience on Oreo or later ROMs than on Nougat. I can reliably get Case 3 with Lineage 15.1, much more hit and miss with stock or Lineage 14.1 (both 7.1).
My big issue is actually audio dropouts. It is not a pleasant listening experience when I can get it to work. If I can get WiFi Launcher working, will that provide a better audio connection? I do have a shorter high quality Anker cable on order from Amazon in the event that cabling is the issue, but any ideas on how to reduce dropouts would be really helpful.
Not necessarily, audio drop outs are probably caused by slow wifi...