Me too, on 2 apps in our portfolio... Showstopper. Posted a feedback: FB18876143

This is amazing!!! I ran into this issue yesterday and I've spent some hours today to isolate this weird NavigationSplitView behaviour to the presence of a ToolbarItem in the bottom bar. And now seeing your workaround being posted 4 hours earlier is mind blowing! Thanks @domagojbu, you've saved my design!

Yes!!! Thank you, it worked! I did try that before in various places in Xcodes build-settings itself but it never worked. But with your tip of putting it into a xcconfig in the CorePlot project it worked. That is the most confusing thing: getting an error like this in one file and not in my own code that is written in similar way...