This isn't an ARCHICAD issue, but something must have changed in the way your file server and/or network access to it is set up? Perhaps even a Mojave specific issue if you've not changed anything else? For each user's own name to be part of the path to exactly the same file(s), I assume that there is a soft link somewhere in the user space on the server to the shared folder(s). Not what you want, as you're seeing. There should be a common public/shared path to the shared library (etc) that involves no user names. Or, if a user name (login) is required for the server (not uses MacOS server - but peer to peer to another Mac) - it should be a dummy user that everyone uses to log in for access to the shared space. As far as I know, anyway.
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AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB