Samsung has pulled the latest update since it was bricking watchings after a restart.
https://www.androidpolice.com/botched-samsung-galaxy-watch-4-update-bricking/
Multiple user report (via SamMobile) that the new R8xxXXU1GVI3 update for the Galaxy Watch 4 is bricking units. If you happen to install this update, you wouldn't notice anything wrong at first, but upon rebooting your smartwatch, it might never back turn on again, rendered seemingly useless.
https://www.androidpolice.com/botched-samsung-galaxy-watch-4-update-bricking/