This is not a bug. Competitive Leaver Penalty Rules will automatically penalize a player that takes more than two minutes to return to a match, regardless of the match result. It also applies if a player leaves and returns three times or more in a single match. This rule is enforced to prevent a dishonest player from returning to try and minimize the impact of SR loss and bypass the penalty altogether, especially if a miraculous 5 versus 6 win occurs. Details about this and the entire Competitive Leaver rules and why they affect technical malfunctions can be found here: