Playing in the Vanguard Strikes Playlist, we played through most of the strike with a fireteam of 2.
By the time we reach the boss, my teamate drops an empowering rift, I drop a a reloading shield (forgot the name) and we melt it with chaos reach and wendigo respectively.
One-phasing it before the mechanics can start normally makes it so that there is some time between death of boss and encounter death, for all intents and purposes the game doesn't think the fight started yet. As we kill the boss, another guardian joins us, presumably because the fight hasn't started yet according to the game.
Because of this, not all players are on the plate to spawn the boss and thus, the game does not end the encounter even though the Genesis Mind is obviously dead.
To fix this we had to wipe, and then start the encounter again.
Not a huge problem, and don't know if it is an important fix anyways since it wasn't a big deal, but decided to post anyways. Thanks!