I am using the latest donor 64-bit Build 711 on Windows 7, 64-bit (patched up to date).
I tried to backup contents of a directory on a 2 TB external drive towards a new external 5 TB drive.
After copying some stuff manually, I tried to use the compare / synchronize feature (no filters, plugins etc. setup and Freecommander has just been installed)
Unfortunately the file/directory lists remain empty after scan is complete although both sides clearly are not identical, see the image below. While scanning it counts rougly 8300 files or so, if I remember correctly.

At the bottom of the menu there are some numbers listed (possibly number of files identical or missing on either side?).
Can you please have a look?
Since the lists remain empty, Free commander would not copy any files in order to synchronize.
I have also tried to use "*" or "*.*" in filter include settings, but it does not help.
The problem is also present with all currently published public 32-/64-bit versions.
Additional hint: I have very little disk space left on the source side (right side in screenshot, drive E:), just a few MB. That should have no impact though (plenty of space left on drive C and other drives).