The "cracking" for me has spread to Pandora as well--in other words, streaming music.
So, the only compliment I can pay Microsoft is that Nokia's tech support has dutifully called me, on a weekly basis, to assure me that my case is escalated but they don't know how to solve it. I'm not being ignored, I just can't be helped.
So, I'm giving up. I'm going to flash the ROM of my phone back to 8.0--in other words, the version where playback worked, and internet sharing did as well. Cortana will have to go until I get another phone--which, after this 4 month experience since 8.1 first dropped, I'm fairly certain it won't be a Windows Phone. Microsoft can't give me a guarantee that one of their updates won't break two important functions on my phone, with no way to roll them back--I suppose no company can, but I'll give Android a try until they pull the same stunt and drag me along for a few months with no solution.
I guess it can't be helped. I'm a little disappointed.