Apple Watch Series 3 Storage Full with "Other"

I've had my Apple Watch Series 3 for only 15 months. I have barely any apps on it and only use it for workout tracking. However, 7.6 GB of 8 GB shows as full and the large majority is an "Other" category. I've started getting pop-ups that my Storage is Full on my watch. When it does this, I can't track any workouts or use the watch at all - even though I barely have anything on the watch and can't control the Other category. I've tried rebooting it multiple times a week, but that doesn't reset the storage. How do I fix this Other storage category so that I can use my watch?