Theres always like a little lag at the start of games in HC Search when everyone runs forward as soon as you spawn, i think depending on your teams connections, whoever has the better connections has the least amount of lag giving your team a non laggy start which adds on about 1-2 seconds of play time, so yeah thats what i think it might be.
Actually I thought that was the problem... But after comparing connections in hundreds of search games I realized that it wasn't always the team with the better connection that would spawn first.