Sometimes GC sync sucks big time!
Had problems with unstable sync between ios and web. Signed out of the ios app in order to align the sign-in on the two platforms - still using identical email addresses.
When signing into the ios app again (still same email) 4 months of training and some lovely hiking data was just gone.
If you have a smilar problem, I hence cannot recommend my methods of signing out of ios app. Make certain you have a backup of training data first.