Once exported, when uploading it on Garmin Connect, Garmin says "We don't support the file type you tried to import.".
Also importing and loading the same exported file in FitEdit does not show the heartrate chart, so I suspect there is something wrong with the exported file.
Steps to reproduce
Export only works if another file is imported, loaded, exported and unloaded first (see https://github.com/endurabyte/FitEdit/issues/12).
Once exported, when uploading it on Garmin Connect, Garmin says "We don't support the file type you tried to import.".
Also importing and loading the same exported file in FitEdit does not show the heartrate chart, so I suspect there is something wrong with the exported file.