It's possible you have a second ''tab group''. This article describes the concept: [[Use Tab Groups to organize a lot of tabs]]. To work with the tab groups in the current window, press Ctrl+Shift+e or look for a menu button toward the far right end of the tab bar. If you find multiple tab groups, you should be able to drag all the tabs into a single group so you can work with that one group and see what is getting closed. I don't use this feature myself, so if that doesn't work, hopefully another volunteer can provide a better set of steps.