Same here. I've been using Spotify remote from my Gear S3 for at least a year and now all of a sudden it stopped working. It will only connect via Wifi as a standalone but the remote function won't connect to the phone app via Bluetooth.
Settings show my Gear and phone are successfully connected via Bluetooth. Whenever my Gear notifies me that it is 'Unable to start Spotify - connect to Bluetooth to start listening', the Spotify app launches on my phone - but that's pretty much the extent of the connection.
I just upgraded to a Samusung S9+, but the remote function worked fine with the new phone for a week or so before stopping. I've tried re-installing Spotify on both phone and Gear, but so far I still can't use the remote function... :'(
I have the same problem. Thought It was because of my phone. I have a Samsung galaxy watch 46mm with an Oneplus 3T. Good to hear I'm not the only one. Hopefully spotify will take a look at their app on Samsung watches.
I have the same problem with Samsung Gear Fit2 Pro's Spotify app, the remote mode stopped working some time ago and when I select the remote mode, it loads for a long time and then throws a message: "Unable to start Spotify, Connect to Bluetooth to start listening", although my Gear is connected by Bluetooth and other synchronization works.
At quick glance there are a few topics dealing with this same issue with different Tizen-operated devices and someone seems to have found a solution over here, by rolling back some versions of Spotify on the phone. I haven't tested if that works, but feel free to try if you like. I think I'm just going to wait for an update.