Some Samsung Galaxy Watch4 and Watch4 Classic owners have been dealing with a particularly bothersome issue. After the R8xxXXU1GVI3 firmware update was released, some smartwatches refuse to turn on once they've been shut off. It's forced users to keep an eye on the charge of their Galaxy Watches.
The issue doesn't seem to be affecting everyone, but Samsung has stopped rolling out the update in various markets and will be releasing an update with a fix soon. If you have the firmware update and haven't noticed any issue, it still might be better to err on the safe side to be sure.