Same for me. I use it to run and I never had this issue with the 5 series apple watch. I upgraded to the 8 because of the usual apple charging bs. I'm using the iphone 13 pro that I've had for less than two years. A couple weeks ago something popped up on my phone saying my camera may not be an authentic apple product!?¿... I replaced my iphone 11 pro because it was popping up an"unable to download" (even though I wasn't downloading anything!)message every day that I couldn't get rid of, after less than two years of use...I am really starting to see that their products are designed with planned obsolescence so frustration leads to faster replacement. Sorry I know this isn't exactly helpful.
I unpaired and re-paired the watch yesterday, then reset my phone & only after that did my itunes finally update on the watch. I noticed the settings in my watch had "add playlists songs" toggled off. I turned it on and have to turn it on daily because it seems to turn itself off.
Hope your watch starts acting right. Super annoying .