I have turned off all community packages apart from project-manager, recent-projects, tool-bar and flex-tool-bar. When I start Atom there is no problem and I can see the files tab bar. When I select a project from the recent-projects grid the tab bar disappears.
The only way to get the tab bar back is to disable/enable the core tabs package. A real drag when you are hopping from project to project. I am not sure which package is causing the issue so I also reported it on the tool-bar bug page.
Thank you for any help you can give.