Cubase 13 Panning fails on CB12 projects

I have projects that were open in Cubase 12. Everything works fine. PC, Windows 11. Mono tracks to stereo group. No plugins or inserts. Standard group bus routing. L/R pan works exactly as expected. When the project is opened in Cubase 13 however, the mixer channel Pan setting is ignored and everything is Mono in the group bus no matter what I do. It appears to be simply ignored.
If I add new track in the Cubase 13 project and then physically drag the wave information to the new track then the whole problem goes away and the Pan works normally.
Obviously I can’t re-create every track in the project and basically lose what I have, any ideas? Any help would be appreciated.