AutoSync passes through the FIT file the device uploads to Garmin Connect. No file, no sync. It does work differently with other apps based on how they implemented it.
Rodney just wanted to update and say I accidentally found the way to make it work, I've only done it once and maybe it was a fluke but well it sync'd a manual workout today from garmin to TP.
In modern to manually add you can either click the + on the activities widget thing OR once in the listed of activities that looks like how the old version of connect showed them you have the manual add or import buttons at the time. By selecting that manual add you get a much more detailed form for the manual add. For example I was adding a swim this morning and that had a box for pool length and after having put my yardage in with with it showed how many lengths were done, not that I care just neat.
Anyway I saved it as usual to go manually upload to TP and sure enough it was there already!
I have nothing else to add at the moment so I haven't confirmed it but will do so in the morning and update if needed.