Ok, I have bought a new iPhone 13 and transferred my stuff from my previous iPhone 7+. Everything is working fine, except for the Fitness app which displays nothing but a static message that tells me I need to setup Activity on my Apple Watch. I have a Watch series 3, which is syncing data successfully with the Health app, but not Fitness. Calendar and other apps are syncing. If I were to unpair and reset the watch would that fix the problem and would I lose my existing fitness data by doing that? Rebooting both devices didn’t help, nor did upgrading the watch to watchOS 8.
Ok, so the watch seems to sync data with health. The question to me is what device the watch uses to sync with Health: the iPhone 13 or the iPhone 7+?
Does the watch show up in the watch app on your new iPhone 13? If so: if you change settings in the watch app on your new iPhone (like a watch face), are those changes being applied on the watch?
If you start the Activity App on your old iPhone: does the new Activity data show up on the iPhone 7?
Regarding your question about data loss: it depends on your setup. You should be fine with data that has been synced to Activity on your iPhone, especially as long as it is being synced to iCloud or whatever. There is a possibility to lose data that has not been synced to an iPhone. As far as I know the watch does not sync data like that to iCloud on its own.
It is complicated. Something went wrong while “transferring” your data between your iPhones. What method exactly did you use to transfer your data? Do you backup to iCloud? Is your Health and Activity data being backed up to iCloud?
You basically need to make sure that all your Fitness and Health data is being backed up to iCloud (that would be my way). If you are 100% sure about all that data being backed up in iCloud, you should be fine with unpairing and pairing the watch again.
Maybe somebody else has more ideas.
Since I posted I have discovered the interesting fact that the Fitness widget in the phone’s dashboard mirrors the data from the watch, but when I tap on the widget I get the app as previously described.
In the light of that it’s clear that the data is being sent to the phone from the watch, and presumably backed up to the cloud. I doubt whether repairing would have any effect. It looks like a bug to me.
I think a fresh install might help, I assume you already tried restarting both devices