For other people who's Galaxy watch fails to pair around 75-80% here's what fixed it for me.

I had this problem with my gw4 classic and literally spent hours trying to fix it. I cleared my phone's system cache, reset the watch, reset network setting, cleared the cache on play services, un and re- installed wearable and more. Nothing worked. Until now, I did two things and I don't know which fixed it. I gave play services access to all the permissions and I cleared the play store cache. After two and a half months of not wearing my watch and everything I tried that was what finally fixed it..