This is common not just for us. There's something about a rag tag crew banding together and over performing for a stretch, but it generally doesn't last long term. Could be that the players can see the weakness so they adjust their game accordingly to compensate, but eventually they become comfortable again and fall back onto bad habits.
Real life example that I've seen over and over again is a team having a weaker goalie start for them, so the whole team puts more effort into limiting high danger chances. I had a player once have to start 3 games over a season because our starter couldn't go, guy wasn't a goalie and it was very obvious but we were in a pinch, posted 2 shutouts in his 3 games. Our starter, who is a legitimately good goalie, hadn't posted a shutout in over 2 20+ game seasons up to that point. We've seen it with Hutchinson's and Brossoit's runs with the Jets too, team plays differently in front of a backup when they don't entirely trust them, then they become complacent and return to their game and the goalie returns to their normal numbers.