Need to back up a bit ...
I never mentioned sharing a front end. What I said was that if I had the FE open already and then clicked a shortcut to the same FE file that I already had open, I got two instances of the same FE running on my computer. The shortcut did not notice that the FE was open and shift focus to that like a shortcut to a Word document would do.
Somewhat annoying to me, but I don't know that myself (or another user, not AND another user) having two versions of the same file open would cause an issue.
I can see User A and User B both having the same FE open on the same network causing an issue. They select another record and the front end jumps for the other user.
Why are you allowing this to happen? Users should NEVER be opening a FE on the server. That you can check also.
This was a hypothetical. User A and User B opening the same FE could be an issue, but is not allowed (any more - it was previously before I learned on here how to prevent it). Now, half our users use Citrix and they open the front end from their own mapped U:\ drive which I'm assuming would be considered on a server, but it is their own copy of the FE. I'm assuming this is not an issue and I don't know of another solution since they can't write to the Citrix desktop. We've been using it for a long time, but that doesn't necessarily mean it is safe.
I go one step further - I specify the location of the front end on a users machine
I do this also now. Has to be on the desktop for local users and the U:\ drive for Citrix users. A bit Draconian, but so far everyone is okay with it.