Hello there. I think I may have the answer to your endless buffering issue as I had it to on my brand new apple watch ultra with cellular.  One day it worked, the next day it said endless buffering. Rebooting and re-installing did nothing to fix the issue.  Both iphone 13pro and apple watch ultra were 100% up to date.  The fix is too easy.  Please do the following: launch pandora on your apple watch keep hitting the < left arrow carrot until you get to the main pandora screen on your apple watch. At the very bottom it will say in Gray Playing From.... and it will probably say (phone) Now the fun part. tap on phone and change the checkbox to Watch. It should now play just fine from your watch if you have Bluetooth headphones connected.  It worked for me anyways. Hope this helps out someone because this thing was driving me mad. I went through 3 uninstall/ re-installs of pandora, and around 10 reboots of both my iphone and apple watch.  It works great now.  Good luck!  -Mark ... View more