Soul-DM even when downloading through the terminal its pretty slow for some reason but only with eopkg not with flatpak
As brent noted, the RIT server sometimes gets bogged down right after an update releases. If you hold off for a day (or two), when every mother's child isn't trying to download the updates at at the same time, you'll probably have a better experience.
Soul-DM /install/usr/share/spotify/libvk_swiftshader.so does not exist
I'm not sure what that is about, but it is something to do with the update process for Spotify. I'll see what I can find out, or better yet someone who uses/maintains Spotify will come along with an answer/workaround.
A thought: Since you use Flatpaks, as I do, you might want to uninstall Spotify and then install the Spotify Flatpak. Flatpaks, as you know, are self-contained and more-or-less independent of the operating system.