Have you tried turning it off and on again?

Seriously though, this has sorted the occasional glitch with my watches over the years. The last time I wouldn't receive haptic feedback when notifications popped up. A quick off/on sorted it.

The above advice is a good starting point. I'm on the Garmin beta program so I receive frequent software updates on my wearable. Its been standard practice now to perform a soft reboot (off/on) after every update. These devices don't get turned off very frequently so if there's an app that's being a bit of a memory hog it always helps to do a restart occasionaly.

Press and hold the side button and the digital crown, until you see the apple logo. Should give it a reset and and get its collective stuff back together. 

Mine's been fine sine the last update, for what it's worth.