same here, was winning a game, and then it happened, seriously this website is a joke.
502 ?? Server error. Our fault. We will look into it!

The server went down in the second move and now that is back I lost the match and the rating points. Is there a way to contest this and get the points back?

Yup, it was done for a bit (like, REALLY recently). The website has been getting a lot more traction as of late, partially due to The Queen's Gambit on Netflix, it's getting a lot of people interested in chess and, of course, they come here. As notmtwain said, they had a million new members just last week. Lots of traffic.
happened to me again soo annoying