I've downgraded spotify on my phone to be able to use remote on Gear S3. Yay, it works again.
With latest Spotify app on the phone (S8), when connecting from Gear, a notification bar with Spotify shows up for a split second and immediately (<1s) disappears.
With the downgraded Spotify app on the phone, the same notification bar shows up and remains in the notification area. The message on the bar reads : "Application null is connected."
"null" in a user-targeted message smells like a bug, either the party providing the content is messing it up (Spotify app on Gear?) , or the recipient (Spotify app on the phone) does not know how to treat the message with missing application name...