um, have you tried to export all your raw data from garmin? i have 15 years of logged data, and that dump does not include any fit/gpx/tcx files. it was 196 json files (228mb) which are just high-level summaries. using one of the hacky third-party export libraries, i was able to get the actual fit files (5708 files, 373mb). even that has missing files, empty files, and duplicates. very frustrating.
the lesson i learned is you can't just expect these exports from any online services to be complete or what you expect. i highly recommend going through an export of anything you depend on and see if it has what you expect.
This is particularly relevant with the recent blue triangle of death episode where all their newest watches downloaded a corrupted gps ephemeris data file and entered a boot loop.
One of the recommended fixes was a factory reset of the watch, which deletes all of the stored .fit files.
the lesson i learned is you can't just expect these exports from any online services to be complete or what you expect. i highly recommend going through an export of anything you depend on and see if it has what you expect.