Running into the same issue on Manjaro KDE, and found the same solution. Gotta say the age of this thread and the lack of responses doesn't give me hope for this being fixed anytime soon, but I'll drop some extra info in hopes of boosting the issue and getting the client working.
Interestingly, my client does successfully log in, but the window remains blank and non-functional. If I play music on another device, I still get track notifications on my computer. In addition, if I select the computer from spotify connect on the other device, sound will play as expected; alas, the window remains useless throughout all of this.
When starting Spotify from terminal with --show-console, I see quite a few errors, but none of them are especially descriptive. Still, most of them seem to be related to the login process, so I imagine it's likely they're related.
The first one is as follows:
16:58:16.975 I [f:245] aq: on GoOffline[Offline] -> [Offline]
16:58:16.975 E [f:221] aq: OnError reason: 3, error:User requested disconnect
16:58:16.976 I [f:245] aq: Disconnected
16:58:16.976 I [f:245] aq: on GoOnline[Offline] -> [Online]
This only happens once per launch, and appears to correct itself.
Next, there's this:
16:58:17.334 E [connect:471] ConnectConnectivityListener: received empty connection_id
16:58:17.334 D [connect:953] Connection lost
This one shows up three times for me
Another one is this:
16:58:18.397 D [connect_dial:423] DialDiscovery::checkForApp: http://10.111.135.79:8009/apps/com.spotify.Spotify.TVv2
16:58:18.407 E [connect_mdns:311] check for app failed: app_not_installed
This one pops up a bunch, with different IP addresses each time. I doubt this has anything to do with the app not working, so I won't spend any time on it.
Not aware of anything else noteworthy, and this comment is already way too long, so I'll end it here lol. Fingers crossed that they fix the app soon