There is a problem in Mojave. Or more specifically, Mojave and Adobe's apps.

No matter how you connect to any remote device, the Adobe apps will randomly (and often) say you can't save the file, or, write access was not granted. Doesn't matter if it's a server, or even just a shared folder on another Mac.

I had rather recently made Mojave my everyday OS on a 2010 Mac Pro. Saving files open in Photoshop back to the server was hit and miss. Mostly miss. I booted into High Sierra to see if that was the difference, rather than the server. Yes! The exact same, up-to-date version of Photoshop CC 2019 can save a file you're working on over and over without a single error message. But as soon as someone else logs into the server from a Mac running Mojave and opens a file with Photoshop or other Adobe app, the files of the folder that person is in get locked (or something). We cannot be in the same folder. Not even the Mac running High Sierra. As soon as the user with Mojave disconnects, all error messages go away for the High Sierra user.

Locked files (or whatever Adobe's apps, or Mojave are doing), don't just affect the other user, the problem also affects yourself. You can be the only person connected the server, and as long as you're booted to Mojave, you cannot work from the Adobe apps without getting messages that you can't save a file.

When these write errors occur, you end up with hidden junk files that get left behind in the folder. Depending on how you connected to the server, either .afp.deletedxxxx or .smb.deletedxxxx files. The xxxx being a number. These can accumulate by the dozens rather quickly, eating up lots of server space as they're the same size as the image you were working on. Some will be removed by the server when you dismount. Others you have to get rid of manually.

I don't know who's really to blame here, but since it seems to be only the Adobe apps that cause this issue while in Mojave, then I would say it's Adobe that has to figure out what their apps are doing wrong. From the messages you get, it would appear the Adobe apps aren't releasing files after completing a write. So the next time you try and do a save of your progress, it won't let you. Photoshop hasn't released the file, so neither can the server. Bingo, bango, bongo, you get write error messages. That's my guess, anyway.

Apple will also be getting this bug report. Mainly because testing points both ways. It could just as easily be Photoshop is releasing files after a write, but Mojave isn't. But from Mojave, I can be in Quark XPress, and literally any other non-Adobe app and write back to server all day long. It's only the Adobe apps that fail, and lock other users out of an entire folder. But at the same time, the exact same version of Photoshop CC has zero problems writing to the server in High Sierra or older OS. So then it appears Mojave is the problem.

One way or the other, the combination of Mojave and Photoshop CC makes it impossible to work directly off the server. You haver to copy files you're going to work on the desktop, then copy them back to the server when you're done. This is time consuming and almost makes having a server pointless.

Our new 2018 Mac Mini can of course only run Mojave, which makes it nearly impossible for us to work off the server together.

We've tried having the Mac running High Sierra connect to the server via AFP, and the mini as SMB, but that makes no difference. The main issue is if you're using the Adobe apps in Mojave, you literally cannot reliably save a file from within the app anywhere but to a local drive. Doesn't matter if anyone else is using the server. If you're in Mojave, you cannot write to any server or shared drive without experiencing write errors. Worse, just being connected affects everyone else whether the other Macs are using Mojave or not.

For the time being, I've gone back to High Sierra on the older Mac so at least I can write to the server without issue (when I'm the only one on it).