If you have tried the update to 10.14.6, does it fix this problem? If I recall correctly, the 'fixed' items list said something about fixing an SMB problem.
I run my weather station updating app on my headless Mac mini 24/7/365. Today I saw some text I needed to change in one html file.
Next task was to save the file on the mini. No problem, just click on the Mac Mini icon in the "Locations" list in the Finder Side Bar.
Well, since
Mojave macOS 10.14 that doesn't work normally because Apple has decided that its own file sharing system (AFP) wasn't as good as SMB. Naturally, this means we have to manually type in the SMB address for the shared disk if it's been too long since we've shared with it. (If you know how to get Mojave to remember each of the shared devices instead of just adding to a list that starts deleting the oldest items after a certain number is reached, please let me know)
Unfortunately, even that manual method would not work today. Fortunately, that particular page only gets updated twice a day, so I had some time to 'play' with different incantations and chicken sacrifices.
What finally work, this time, was to access the mini via File Sharing and opened Sharing Prefs->File Sharing->Options. Surprisingly, under the Share files... using SMB, there was text showing that there was 1 user connected! Well, someone had certainly tried to be connected, but somehow the OS wasn't co-operating.
With the Options sheet open, I
UN-checked both the SMB and the AFP checkboxes. I also
UN-checked the only user in the Windows File Sharing list. The result is that "File Sharing" is totally disabled. I didn't even bother clicking "Done". You will see that Service is unchecked and you may see that the external disk disappears in the Locations list if a Finder window is still open.
I then
RE-checked SMB and
RE-checked my name in the "Account" list. Now things should be back to normal.
