Why does chess tempo fail at random; what is the biggest free database online that is reliable Sometimes chess tempo works.  Sometimes it does not.  Seems random. Is there another database that is completely reliable that is as big as chess tempo?

I am looking for a DB that gives the moves with winning percentage or else percent results for  WDL for each move.
This fits the bill perfectly, and ChessBase is incredibly reliable:

https://database.chessbase.com/

You will have to create a free account, and there are features that are premium, but for winning percentages, it has that for free. I am logged into this with a free account and you can see the percentages in the screenshot.



Here is what it looks like with my paid account (just the right portion of the screen changed, so I only took a screenshot of that).



Chessgames.com also has what you are looking for in terms of percentages here, but with much fewer games: https://www.chessgames.com/perl/explorer