I have encountered exactly the same issue on GCM version 3.2.0.26 on IOS on IPhone 7. The Performance Stats menu was there for a few days, and suddenly its gone. I got a new FR935, which added many new GCM menu options, which included Performance Stats, but now its gone. I didn't notice it was missing until I paired the new RD POD, but that may or may not have been the cause. Any solution to the missing content from the GCM APP?
It's been around a week since my performance stats disappeared from GCM. Is Garmin working on fixing this? Restarting phone, app or my Fenix 5 does not help. Frankly I'm quite surprised not many people are reporting this problem. Though it seems more like garmin connects problem since I can't find my Training Load on my GC page.