I believe this started after last weeks update on Tues (6/8). I also believe this is related to the search service. So I normally launch applications by hitting the Windows key and typing the name and hitting enter. But now it will do the search, but hitting enter or clicking an app won't open it. Also, sometimes if I pause for a few seconds the start menu closes itself. I can still open things the manual way or by using the run dialog.
Also, hello from the past. It seems my last post was in 2013. It's good to see the site still going with many familiar names.