I received a reply at the time from garmin...After reviewing information from engineering: it is possible for the activities uploaded more than a year ago to lose the detailed information.
They suggested using my watch to respond the data. I had deleted it from the watch.
I just transferred over to strava instead back in 2014 and no issues since. To be fair I don't think they've "dropped" the map detail of any of my other data since.
Regards
Dan
Is there anyway to get this data back?
You could try exporting the Activity as Original, deleting it from GC, and then importing back from the file.