It seems that segments crossed are sometimes not picked up when an activity is loaded. It would be useful to have the option to re-scan for segments when you know that you have crossed a segment that has been missed.
I agree. My Connnect synced with all the segments I crossed one time, but hasn't picked up any that I've crossed in the last several months even after I went to Strava and made sure that my accounts were linked.
I'm no authority on the matter, but I believe that if you download the activity from Garmin Connect, delete it, and then re-upload it, it should be re-scanned for segments. It isn't ideal, but it should work.
Yes, deleting and reloading does generate a rescan. However, if the segment was created from the activity that is being deleted, the segment is deleted as well (and yes, I have had segment data not recognised even though the segment was created within the particular activity).
