Good read on Bleacher Report:

but the main point that I thought we should focus on was, once again the awful second half play. Something that's becoming all too familiar for Steelers fans.

After racking up 10 first downs on 226 yards, and punching in 17 unanswered points on the first three drives of the game, the Steelers gained just 144 yards of total offense on their last eight drives of the game.

After leaving the locker room at halftime up 17-3, the Steelers gained just 70 yards of total offense and punted the ball on all five of their second half drives.

If the disappearance of the Steelers offense wasn’t enough, the defense played Copperfield all game long. Never truly leaving the room, but often times absent, the defense gave the Jags and their 22-year-old rookie quarterback room to hang around until a Hail Mary ended their late-game efforts.
I just don't know what it is. In 2008-2009, we were the comeback kids. Always awful in the first half and unreal in the second half. Something has changed this season. The first few series of almost every game this season, we've looked good, and then we've let up after the first quarter. That is going to be trouble later in the season..