I haven’t used these synced dirs in a while, so I don’t know how long it was broken. (EDIT: I have used the dirs, but not confirmed the sync.)
When I noticed the problem, I manually upgraded the brew install “1.8.0_1 -> 1.9.0_1”. I also noticed that one of the docker syncthings was 1.8 and upgraded it to 1.9.0. The other docker syncthing was already 1.9.0, perhaps due to my habit of upgrading a larger docker-compose file. (Again, those two linux docker syncthings were happy with each other.)