I've found an issue with Start10 where the start menu closes when I left click 3 times on the empty space underneath pinned shortcuts.  The issue does not occur if you on the right column or near the user name at the top of the menu.  It is strictly contained in the area that I've highlighted in green on the sample picture.

To replicate the issue, you can set Configuration to allow space for 20 large icons and click in the area that has "settings" and "microsoft edge" listed.

To speed up the closing of the start menu, right click on that empty space to show the context menu and then left click on the empty space next to it on the start menu and it will immediately close.

https://www.dropbox.com/s/fxmzjnikwotn3dp/Start10.png?dl=0