I don't think either goal was necessarily down to individual errors though. The corner certainly wasn't, that was clearly a training ground routine. Haven't gone zonal all season, but we suddenly do it when things were improving in the set piece department? I don't understand that change at all.
The late goal came from the constant tactical changes. We know Koulibaly cannot stand up against players in a 1v1 anymore, this is why he has the 2 cb's next to him, but Potter took one of them off and exposed Koulibaly right at the end.
That is more of a tactical error than a player error. It's not a good look for Koulibaly, but we have known of this weakness since the start of the season and adjusted our game to protect him, Potter threw it all out of the window right at the end.