@aflag , you may want to check out this recent post, as well as, some of the earlier & subsequent discussion in another thread because I think getting Binder to open the right notebook with JupyterLab using a link and workspace behavior may be related.
It seems dependent on browsers. Perhaps? I’m still unclear 100% on that since my version of Firefox was old. Besides that, one work-around is to encourage your users to open things in incognito/stealth mode. Or encourage them to refresh, (see below). Or try to leave (or demonstrate) guidance on how to navigate to notebooks.
The @dlukes here in the original post in this thread said reloading helped. And indeed Command-R on my mac in Chrome did trigger a hard refresh and correct loading of the specified notebook (via workspaces behind-the-scenes) in a MyBinder launched instance when I already had a fresh instance launched in another Chrome window.
You don’t say if you are actually using JupyterLab locally or through JupyterHub. The initial post said JupyterLab locally was fine. So I assumed you were using JupyterHub. Binder is a public BinderHub, which is a JupyterHub with extra tech (such as repo2docker, etc.) and so some of the findings with Binder and workspaces, I thought may be pertinent and that’s whyI redirected you to that other thread.
You also don’t say which version of JupyterLab you are using. I’m still still not sure there isn’t an issue with workspaces in JupyterLab 3. See my ‘caveat’ here where I describe that none of the ideas seems to be allowing the JupyterLab demo from the ‘Try Jupyter’ site Project Jupyter | Try Jupyter. So maybe the work-around would be to use older JupyterLab? Don’t know for sure on that as this uses an imported workspace and others don’t.