Apple Watch Ultra screen goes black when using the Fitness App

About once a week when I go out to exercise the screen will go black at the beginning of the workout. I can still feel vibrations from timers and my Intervals app. I usually reset the watch, but it will keep going black until I can sit it on a charger. It started happening a few months ago, so I'm wondering if there is a software fix for this or will I need to get a new watch.