Ending up with a Resync of already Synced data

[syncingfeeling]

I was originally a Free user and I had created a Read Only sync between two computers (which act as local to each other, but are connected via VPN). I upgraded to Pro and in the process I wanted to change the sync to be an Advanced folder. Being new to Sync I couldn't figure out how to do what I wanted without removing the folder from Sync completely (which removed it from the Sync interface on both computers). I then added the folder back as an Advanced folder, and then Connected it on the remote computer.

The problem is the remote computer is now syncing already synced files back to the local computer, and I don't understand why. Everything was already fully synced -- shouldn't Sync be able to index everything and recognize that the data is all the same?  It's over 40GB of data going over my VPN (ie, it will take a while), so I'm not thrilled about this dynamic, and I thought Sync was built to preclude this sort of thing.

Undoubtedly there's some user-error at play here, so I welcome any input on how to avoid having a re-sync of my data.

Thanks!

[Helen]

Indeed, if the files are the same, Sync will not re-sync anything. 
When you connect to peers with some pre-seeded files, Sync will rescan the shares, hash the files (you see Indexing.... in UI) and then merge these files with remote ones. Merging means that Sync compares files' hashes on both peers and checks if anything needs to be synced. 
So, two questions to you: 

1) do you really see files' transfer or you just see upload/download queue in peers list without traffic
2) check shares' paths in Sync: make sure that they indeed point to the existing directories on your computers. It's a popular mistake - people connect the share to a default location, new directory gets creates and thus files re-synced. 

[syncingfeeling]

Great questions!

1) Yes, definitely seeing actual file transfers. I can confirm this by the amount of data being transmitted to the local computer (I have a bandwidth meter), the prescence of !SYNC files in the .sync folder (on the local computer), and that some files have already been replaced (indicated by copies ending up in the Archive folder of the local computer). Strange thing about the copies in the Archive folder though -- they have a modified date of the when the sync occurred, and not their original modified date.

2) I can confirm that the paths of both ends are correctly pointing to the actual folders, and not some other location.

I had not done anything with these video files, and they had been in sync (in Sync's eyes) prior to my upgrading to Pro and the above described steps I went through.

Thoughts?

[Helen]

Then please submit logs to support, here's instruction. If your logs haven't rotated yet and still hold records for that dates, no need to reproduce that issue again. Just please indicate from and to which peer and which files (share) have been resyncing. Thanks.  

[syncingfeeling]

Great, thanks!  Logs submitted. Support request #53865.

[syncingfeeling]

Just wanted to share an update for the benefit of others: The issue turned out to be that my old NAS was too slow to keep up, and so was throwing all sorts of errors resulting in Sync having difficulty getting files written correctly. So the primary problem was hardware related in this case.