The St. Louis Blues have been Jekyll and Hyde all season long in 2018-19. It should come as no surprise that their power play unit has reflected that overall play.
The Blues have been just as up and down throughout the year on their special teams as they have in their overall play. You might argue the penalty kill has been solid all year, but the power play has been anything but.
The issue the Blues have with their man-advantage is they either seem to score or look absolutely awful. There is almost never any kind of middle ground from which to work off of.