People keep harping on how tired the Bruins are but by this time of the season every team is tired & looking ahead to the All Star break. So no, no excuse there as far as I'm concerned. I think
@ODAAT is correct, all that winning covered up problems that are now being exposed by other teams.
The power play is not working anymore. They struggle to enter the offensive zone and once they get there they spend too much time passing the puck around waiting for Pasta to get open, often making one pass too many that either results in a clear or a short handed bid. Everybody knows what they're going to do now but the Bruins can't/won't adjust. This has to be fixed.
5x5 they're drifting back into settling for perimeter shots instead of attacking the net. And as
@ODAAT mentioned, the wingers aren't coming back often enough or fast enough to help the defense move the puck up the ice.
Hopefully after a good rest they return from the All Star break ready to work on fixing these issues.