Almost 2 years ago, under financial strain post Covid, Wyze changed their Subscription tiers.
No subscription - Thumbnails Only, 5m Cooldown, No AI
Cam Plus Lite - 12s Video, 5m Cooldown, Person Detection, limited to select compatible cams
Cam Plus - Full Length Video, No Cooldown, Full AI Smart Detection
As cam firmware and apps update, the server has been catching cams on the old legacy plan and correcting them to the new tiers above. That is why you have been seeing them go to thumbnails over time.