Downloaded on Apple watch will not play without stuttering (Spotify and Apple Music)

I currently have this Apple Watch Ultra 2 (2022) (WatchOS-version 11.5). Downloading to the

watch from (for instance) Spotify is no problem, but music is stuttering when I go for a walk/run outside without my IPhone (13Pro, running OS 18.5). The same occurs to Apple Music and downloaded content from Apple's own podcast-app by the way! Must say that usually stuttering ends after say 10 minutes, then resuming continuously playing the rest of the run. Having this problem for quite some years now (my older watch my son is using, is have the same issue (same WatchOS version 11.5, Iphone 14). He considers even to go walking this his Iphone in an arm strap! So 2007. Really frustrating, just as for the rest Apple watches (devices in general) are always stable and smoothly working. Tried countless workarounds… but this is my last hope. It amazes me that Big Beautiful Apple has still not managed to tackle this problem successfully in all the updates that passed in the meantime. By the way I use Apple Pro 2 Headphones as well as B&O EX (both have the same issue, does not seem to be Bluetooth related). Suggestions are of course very, very, welcome!