Playing for Brighton is not the same as playing for Tottenham. Brighton can lose games and nobody cares because they are expecting to lose games. Their target is safety, anything else is a bonus.
Here there is pressure and Bissouma isn't playing well under pressure. Conte's rant from last season is coming true again:
“They are used to it here, not playing for anything important. They don’t want to play under pressure, under stress.”
Bissouma looks every inch a player who is not used to playing for anything important. He's not used to having to produce a top performance in every game. One game he's Dembele, the next he's Paulinho. There's only so much a manager can do if a player doesn't have the fire inside.