Child Apple Watch location not updating in Find My app

My son has an Apple Watch SE 2nd gen with cellular service (T-Mobile). Even with his location services turned on (Share My Location is on in the Find My app), his location with the Apple Watch only updates intermittently and I can't force it to update in any fashion (restarting the app, for example). Doesn't matter whether I'm using my iPhone or using his iPad. This is NOT because he is turning the sharing off -- I can verify on his iPad that his location is being shared when he is out of the house. We have restarted his watch, etc. Only thing I haven't tried yet is a factory reset.

What is the solution here? This is a safety issue -- if he is out on his bike, for example, we want to be able to find him, contact him, etc. That's the whole point of him having the watch.