I am still having this problem, last time was yesterday, 21 Oct.
I was very surprised to see so many different forums had the suggestion that removing Avast was the fix. I took my time and ignored those people long enough to find that rebooting in safe mode clears up the missing Start, but I am still not sure about the number of people stating that the problem never came back after they removed Avast.

It does look like coincidence and people imagining a correlation. Glad I found a more sensible solution, but hope the problem goes away soon.