Apple Watch Cellular, setup with Family Setup, missing Activity App

My two elementary age sons started school this year, one of them at a school that's 20 minutes from home. My wife and I have been reluctant to give phones to our kids for many reasons, but after several weeks of deliberation we decided the Apple Watch Cellular with Family Setup looked like a good solution to be able to track our kids' locations as well as communicate with them while they're away, without all the baggage of a full-fledged smartphone. I setup two Apple Watch SE (Cellular + GPS) watches with my iPhone running iOS 15.0. Both watches have been upgraded to WatchOS 8.0. I went through all of the steps carefully to accept and agree to everything including Activity tracking and setting Activity Goals. Both watches seem to get through the process and work for the most part. I finished one watch without a hitch, everything seems to work as expected. The second watch, once the initial setup is complete and I begin to customize the watch for my son, i.e. setting up watch faces, adding a few apps etc, eventually suddenly loses the Activity app. It disappears completely from the watch. It's not listed in the App list, any Activity complications do not render, and the "Activity Digital" Watch Face shows the rings, but when the rings are tapped, they do nothing, and the progress numbers all show '---'.

Activity App is missing from the App List

"Activity Digital" watch face shows inactive activity

Activity Complication missing

This happened with the first setup and I was determined to resolve it, so I reset the watch, unpaired it from my phone and went through Family Setup one more time. I made sure to accept all conditions etc and setup the Activity Goals, I made it through the setup and I saw the Activity app, so I thought all was well. Then after some amount of time while customizing the watch again, the app suddenly disappeared again. Restarting the device does not help. And apparently resetting and repairing (not restoring from backup) does not help. One interesting thing I noticed is that when this "event" happens, my personal Apple Watch that is paired as "my" watch in the Watch app on my iPhone suddenly stops tracking my activity and fitness at the same time. I noticed none of my rings were progressing, so I troubleshot this and found that in the Watch App on iPhone > My Watch > Privacy > Fitness Tracking had been disabled. The Activity app doesn't disappear from my watch when this happens, it just says "activity tracking is disabled". Re-enabling "Fitness Tracking" seems to get me back in working order. I thought I'd try this on my son's watch, but there is no "Privacy" section on his watch's settings in the Watch app on iPhone (via Family Setup), but there is on the Watch: "Settings App > Privacy > Motion & Fitness" where I did find that "Fitness Tracking" was disabled. Unfortunately, Re-enabling this setting did not resolve the issue either.

Fitness Tracking setting enabled

Another note is that I just found that I can't uninstall apps on this watch anymore either. It seems to mostly function in other ways, but something about this watch is acting up. Please help! This has taken up most of my weekend.

For reference, the other watch with Activity App shown in App List