If it's Spotify, not Tidal, it's most certainly
not the same problem.
Spotify and its lossy compression are not a heavy load on the device or on the network. The fact that you still get stuttering only proves that there is some problem somewhere. And with streaming services running (mostly rented) CDN servers all around the globe this
can be tricky to tackle.
The fact that you have no problem with some particular beta firmware version is interesting, but since this kind of problem is very rare with Spotify it's not a foolproof hint at what's wrong. I can't remember if you ever mentioned how you use Spotify with your WiiM. Is it through Googlecast or through Spotify Connect? The Spotify app supports both and the reasons why one fails doesn't say a lot about the other.
While playing something on Spotify on your phone tap the small speaker icon and then tap on the three dots next to your WiiM.
View attachment 23464
This dialog should allow you to switch between Googlecast and Spotify Connect (usually the preferred choice).