Re: Command and Conquer rivals

Each month we have a season. After each season, on the first wednesday of the new month we have a medal reset. All players are set back to bronze and then gain bonus medals based on the rank they were in the last season. If you were master 3 last season for example, you would start the new season somewhere in diamond 3. The -623 medals come from the ranking reset, so this is normal. These stats reset after each week so in a few days this number will disappear.

When you click on Nod or GDI from the main menu, you can see your medals in the top left corner. If you look closely you can also see "Season ends in: X days". Next to it is a little "i", you can press it for more info.

TL;DR: That's not a bug that's normal behaviour after a season reset.