No, it was an outside group ride, unstructured. I did not notice right away it was broken. [Edit, fixed typo]
Don’t know about 4iiii, but with Stages, power spikes are common when the battery runs out.
I’d replave the battery, and clean the battery housing (just wipe clean with dry paper) while you’re at it. Also check that the seal (assuming they are a bit like a Stages PM) is seated correctly.
Maybe you should create a topic but I have never seen an outdoor power curve like that, even for structured workouts ( they look like blunt saw teeth)but I see those sawtooths in virtually all indoor structured interval sessions
I wouldn’t call it a high mileage unit, but the 4iiii on my XC race bike seems fine still. I believe it is a 2019 model.