I have done a lot of troubleshooting, and my conclusion is: after a lost and restored BT connection between Galaxy Active 2 and Galaxy S10+ while Spotify is playing, the Spotify app on the watch and the Spotify app on the phone will not sync again, causing a freeze of the display of song played on both units.
My issues started a few months ago when installing Spotify on my Galaxy Active 2 watch. After I removed that app on the watch and restarted my Galaxy S10+, Spotify worked normal again on the phone.
However, to try again, I did a full clean reinstall of Spotify on the phone as per the linked instructions you gave.
Everything then worked fine with Spotify on the phone, until I installed Spotify on the watch.
At first things were working, the watch app (in Remote mode) and the phone app displaying the played song in sync as they should. But after a few hours it went out of sync, so the song displayed and time of the song got frozen as described in this thread.
I tried to restart the phone and the watch, to not much avail. Working for a short time, then out of sync again.
Ultimately I deleted the Spotify app on the watch and restarted the phone – Spotify on the phone worked smoothly again, also together with by BT headphones Jabra Elite 75+ and BT connection with my Dodge Uconnect 2012 car audio system.
This was a couple of weeks ago.
Now a couple of days ago I got a major update of the Tizen OS on the watch, and I also got the Oct update for the S10+ phone.
After that I tried again to install Spotify on the watch, but with same sync issue as above. I was however able to pinpoint the issue to lost BT connection between phone and watch: after installing the watch app the sync worked as it should. The problems with out of sync appeared when the BT connection between phone and watch got lost due to distance – after that Spotify does not find the sync again between its phone app and its watch app.
Noteworthy though – the Samsung Music Player app on the watch works perfectly well as remote for the Spotify phone app.
Other inputs from my side: any battery saving functionality on the phone has been disabled for Spotify.
Please use this detailed info to recreate and solve the problem, thanks!