Usually this error message occurs when there is a problem between you and the game server. Yes your internet can be fine, and yes the game server itself is not having a problem (if it did the whole lobby would collapse on all players and a different error message would appear). Basically when this happens there is some hub between you and the game server that decided to cut out causing the FTC error.
If this happens once in a blue moon, best thing to do is to play a few games in quick play to see if there are more connection issues, and try again once you think it is safe to play. If you are getting the Failed to Connect error frequently during Competitive games, the best option is to try and carefully test a series of connection tests in Quick Play using WinMTR.
This is a deterrence penalty intended to discourage players from jumping right back into Competitive without troubleshooting the issues. The actual MMR is not directly affected for the two roles not played so the SR is quickly normalized after a few games.