It happens on personal, corp, everything, other machines… etc. I found this can happen as stated above. I could use scp or such, but I’d like it to be easier to “sync”. I’ve tried all the things about (except robocopy) to this point.
Here’s what worked for me…
- Open PowerShell 7.x.
New-SmbMapping -LocalPath R: -RemotePath \\IP-or-ServerName\fileshare -UserName MyUserId -Password 'MyPassword'
3.xcopy "C:\Users\MyUserId\MyFolderOfFoldersAndFilesSource\" "R:\MyFolderOfFoldersAndFilesTarget\" /e- And enter
Dfor Directory when prompted by xcopy.
Haven’t had a failure yet of massive directories since doing this approach vs. Explorer. Woo hoo! I can access the files and edit / save from apps just fine. It was the initial copying that was killing me. I had to put my 1990s DOS hat on to get it to work. 
It was fast and worked. I was able to xcopy a 25GB (including some 2-5GB single files) directory in just a few minutes! Awesome.