Not able to reproduce it. But it sounds like a race condition. That it builds the menu before it has finished loading the TabSession data.
That can happend because during startup MC loads lots of things in parallell. And TabSession is loaded a lot sooner than building the menu. But since things are happening in parallell, then maybe on a system with less cores it takes longer for it to load it and it reach building menu too soon.
There should be a check for it so it waits. But sounds like it missing in some situation. I will check.
Sined they are visible in the Manage Session Windows.. They should pop back if you do something that will re-save them. Because then it will trigger a rebuild of the session menu.
