I FOUND THE SOLUTION!!!!
It even got my friend's activity tab working, that's been dead for months!
I recommend checking your hosts file for any Spotify-related entries.
The file is capable of redirecting traffic for addresses it contains, so it can break Spotify app when it contains Spotify addresses.
It's easy to check and edit, you'll need admin rights:
1. open Notepad as an administrator (right-click - Open as Administrator)
2. go to File - Open and navigate to
3. Choose "All Files" instead of "Text Documents" next to the File Name box. You'll see a handful of files. Pick hosts and click on Open.
4. The file is opened. You will see a block of text with # in front of each line and might see entries like
0.0.0.0 website.com 127.0.0.1 website2.com
Check for any entries with spotify or fastly in the address. Examples may look like:
0.0.0.0 weblb-wg.gslb.spotify.com 0.0.0.0 prod.b.ssl.us-eu.fastlylb.net
(and any variations inbetween)
5. If you do find any, you can delete the line. You can also add a # in front of the line, that's 'commenting out'.
6. Save your changes. Restart Spotify.