Bad coaching.
He's going to get his PP points and 30 points overall and he's shown that with pre and post Ehrhoff. It's his steadiness in his own zone and sudden attacks of bonehead plays that are concerning.
Yes, he makes dumb mistakes. Too many. No stat really shows that tendency. He could definitely improve there but I think it's all magnified by the fact he hasn't had a consistent linemate for 1.5 years.
First of all, although I think he is #1 D-man in terms of ability, IMO he is not a Weber, Doughty, or Suter-type traditional guy who can play 24-25 minutes. If you think about it, this is not supposed to be a top-pair-heavy defence-core anyways, it's not built like that. He's not an economical skater and when he's at his best he hits a lot which takes up a lot of energy.
What he SHOULD be doing is getting his normal ES shift, and the PP time for a total of around 21-22 minutes. This year so far that would be 21:45 of TOI. Like so many on this team he is leaned on to do too much, and now he is used to it. Honestly, I think he's tired. I'd rather see him regain his poise at ES in both ends and contribute to the PP. I don't think he's needed to PK 2 minutes a game, and I don't think it's coincidence that his lapses have occurred in the last two years in which he's been asked to play 24 minutes a game.
Asking him to play less would also reduce wear and tear. Again, coaching.
Coaching comes into play again with the constant juggling of the pairings. It's weird - they trust him enough to overuse him, but not enough to ride out his ups and downs with the same partner.
Also the coaches in regards to taking responsibility when he does make mistakes. Obviously you don't give him the Ballard treatment but a subtle benching here and there could have made a difference. When have we ever seen Edler's icetime reduced, even for just a shift? Or put him on the 2nd unit for a couple of PP's.
Yes, he does get turnstiled a lot - but look at his turnovers. How often is he the last man back who is carrying the puck? Why is he essentially on an island like that? More puck support would help Edler and the entire d-core look a LOT better.
Edler has all the tools, and from what I've read a good work ethic and attitude. So either he is what he is (which I don't believe, I believe he has more upside) or he's missing the proper coaching to get him to the next level of his game by playing to his strengths. I'll go with the latter.