Have you installed even gear s plugin or just galaxy watch plugin? Which rom are you using? Can you tell me exactly what did you do to pear it? Because I've tried with my rom and my Galaxy watch (42mm) and i'm always looping at the end
I followed the instructions from the OP. I did not install the Gear S plugin, as I do not have the S2/3 watch.
I am using the BlackDiamond v.3 ROM (NFE OneUI port).
I uninstalled everything that the OP said to uninstall (1. Gear wearable, 2. all plugins, 3. Samsung Accessory Service, 4. SASystemProviders). You'll have to go into [on your phone] settings -->apps --> include system apps to make sure all 4 of those apps are uninstalled.
I unlinked the watch from the bluetooth menu on my phone. I went on my watch, and went into settings and scrolled to the bottom, where it says "Connect a new phone." I followed the on-watch screen instructions (note: this will wipe the watch). Then I left the watch in pairing mode.
I downloaded the Gear Wearable directly from the Play Store and the FireWall app (note: requires root to use this app, but I guess since you have a custom ROM, then you must be rooted. If you're not rooted, then you're doing something wrong, having a custom ROM but being unrooted). Make sure you do not even launch the Gear Wearable App.
Then I installed the Samsung Accessory Service and the Galaxy Watch Active (in your case, just the Galaxy Watch) plugin APKs. You can find them on apkmirror.com (the most trusted site for apks, except it is filled with ads, but at least it is trusted by the community). Make sure none of the apps have been launched yet.
Then I went into the Firewall App (AFWall+) and I searched for that app (Gear wearable) : all three of them should be under one single row entry. I ticked all 3 boxes for that row. I then tap the settings (3 dots on the top right corner) and hit save and turn on firewall. This will prevent those apps from accessing network functions (cannot connect to internet, cannot update itself). Then I launched the Gear Wearable app and did the setup as normally.
I still haven't turned off my firewall, for fear of being unable to connect back after this tedious setup. There is a guy who posted a video describing this exact process on this thread. You can look for it, although he used the Gear S plugin, I did the same exact procedure but with the Watch Active plugin. I'm sure it will be the case for the Galaxy Watch plugin. Good luck! Let me know if it worked!