How to troubleshoot copies repeatedly not verifying 1st time if path is OK and target is reliable?

[Stilez]

I'm doing a folder copy (as ordinary as they come) from Windows 8.1 to a file share run by Samba. The files are all photos so the filenames are shortish and normal chars, and the target is a nested folder mapped to a drive, so it's copying to X:\PIX\. I have SHA1 verification set, and using latest v18.x.

About 1 in 5 pictures fails first time with a "target + orginal don't match". It often works if I click "retry". A few piuctures later (there's 3000 in the folder) it happens again. I've wiped the APPDATA folder and program folder and reinstalled to be sure. How do I track down the actual issue to fix it?

[highend]

"target + orginal don't match"

Does it show the calculated hashes as well?

Unable to reproduce that behavior (copied 6k image files to my Samba-powered NAS share...)