Competitive Mode has no backfill protocols, so it can be more evident to be encountering disconnections especially when you search for a match.
It may not be just your connection but a problem specifically between you and the game server. Connection tests like [WinMTR tests] help pinpoint issues like this.
https://us.battle.net/support/en/article/27780
Matches cancel right away if the disconnection is in the early part of the match, this is a courtesy to the other 11 players in your match. Now if a minute of match time passes, you have a 2-minute window to return. But really no one wants to play any portion of a match a man down.
Unfortunately all disconnections and game crashes counts as leaving the match and will be penalized appropriately. The game server has no way to discern a legitimate disconnection or game crash from one that is forcefully caused by a dishonest player to bypass leaver penalties. You can learn about this policy here: