Normally, they are among my top programs, but for example, I don't see them here:

I don't see the desired results when I search for Word:

or more specifically, winword.exe:

I can only see the programs again if I force rebuild the index. Then they show up again in the list:

and I can search for the programs as well:

I have not been able to determine when this happens, or what's causing it. Is this a known issue/is there a fix? Thank you.