It then asked me to reset my password as it said it "hadn't seen me sign in for a while"
Anyone else seen this?
I've never seen that in all the years I've been on Garmin apps. Exception would be when signing in with a different account than previously or different from Garmin Connect Web or Garmin Express.
Data is Missing from My Garmin Account After Syncing | Garmin Support
FWIW, there were some policy changes implemented over the past week, which could have triggered this.