You just got the newest software update for your Watch 6 series, like you should do on your phone after an update of wiping cache partition, this also pertains to your watches.
This will eliminate any incompatible left over files that could interfere with your watch working properly. This will not delete any data on your watch. Follow the instructions in the screenshot I am providing. Start tapping on the top button when the screen goes black.
Wiping Cache Partition fir Watches.
