Synchronize through file system not copying update

Joplin 1.3.18 (prod, win32) // on windows 10.
two machines, same config.

Moving data by the following:
a. Joplin syncs to a directory named "d:\joplin_sync" on one machine and "c:\joplin_sync" on the other.
b. Freefilesync and a flash drive are used to sync up the sync directories - and looking at them with file tools they seem to be in sync.
c. But on the second machine, which was set up by loading a joplin image, syncing some of today's changes does not work - the newer file is in the _sync directory, but the sync operation doesn't pick it up.
d. Newly created things seem to go from machine#2 back to machine#1 - about to test going the other way.

The thing not being sunk is a note that machine #1 has and machine #2 so far does not have, as well as a note that is newer on machine #1 than on machine #2.

Both machines are using reasonable web time sources, etc. - the clocks aren't wildly different.

Client ID: 861cbb6a60904cbab2eef22fad712bd7
Sync Version: 2
Profile Version: 34
Keychain Supported: Yes

Revision: 6b75485a1 (master)