I've been banging my head against this and figured it's time I come to the community and see if any Apple experts can offer some advice on what to try.
I've done the following:
The users have their AD Home Folder created, with Modify+Change Permission over all sub files and folders. I've made sure the file isn't highlighted in Finder, and I've also turned thumbnail generation off. I've also turned off thumbnail saving in Photoshop thinking it might be locking the file.
Alas, these things don't seem to change much, I've checked the permission on the file and it says my user has Read/Write access to it. (From the Mac End)
Something to note, we use a local account to login to the Macs but then connect to a server using their domain credentials. We've made sure the keychain is cleared from other usernames and passwords.
We're using Mojave with Windows Server as the Active Directory host.
I've used the SysInternals tool "Handles" to see what is keeping the file open, I haven't nailed it down but when I open the file in Photoshop sometimes I get two handles open for the PSD file, one of them with seemingly no permission, and another with R-D.
When it breaks I notice there is a handle with RWD permission but it doesn't tell me what program has it open since it's accessed through a share.