At some point you will decide to take a look at page 10 of the search results before you actually go through them in order.

Google apparently does not find enough results sometimes to fill all the results pages for a query. It always fills them in order starting with Page 1. (I know this doesn't make sense - the number of results listed at the top of the search usually is tremendous. I decided not to complain - they obviously know what they are doing.)

When you select the results pages in order, you will sometimes come to one that did not get filled completely, or that was just the last one to be filled. You will see that the index of results pages at that point will show only the actual number of results pages.
(Example: 1 2 3 4 5 - there are a maximum of 50 results, 10 on each page.)

If you had decided to jump ahead and pick result page 10, Google would tell you that there are NO results from the search. And all of them disappear. We call this
THE GLITCH. Google has been notified, and is obviously working on the problem (it has improved.)

This can be aggravating, but all you have to do to recover is to click the gray query box in the search bar. Your query will still be there. The search will be repeated and you can continue.

It's easy to avoid this problem -- always browse search results starting with page 1 and don't skip any pages. Not hard to do.