Brown has been that way since college. When he was at UF he wasn't regarded as a hard worker and didn't play as much as he should have due to conditioning issues and ended up as a 7th round pick. From his draft profile on NFL.com:
"That staff didn't feel like he was always reliable as a player. He's got a good ceiling, but you have to factor in that low floor too." -- SEC defensive coach
Scouts call him an "inconsistent worker."
Played just 43 percent of the snaps during 2014 season due to injury and conditioning issues
In his rookie year Von Miller called him the best RT in football and a year or so later he was traded us because we basically were willing to move from the 3rd to the 5th round to get him. He played well here when Scar rode his ass and he parlayed that into a big payday only to end up here 2 years later in a late round pick swap. He has all the talent in the world he is just constantly needs the motivation ($) to play well. Right now the team seems to be willing to pay up to get the performance out of him.