Via Tennis.com:
Rafael Nadal has resigned from the ATP Players Council, a number of journalists—including the New York Times' Chris Clarey and Australia’s Craig Gabriel—reported. Clarey tweeted that Nadal has been frustrated by a lack of support from other players. Nadal told the London Times' Neil Harman in January that he was tired of the aggravation that goes along with being a board member. He and fellow council member, president Roger Federer, have disagreed over issues as of late, such as a potential two-year ranking, the schedule and time violations. 

• This article via The Telegraph says: Rafael Nadal resigns as ATP players' body vice-president after lack of movement on changes to ranking system
• Rafael Nadal Resigned From ATP Player Council Earlier This Month - Via The SportsBusinessDaily

Whatever the truth is to why Rafa has decided to step down from such an important role. I am sure he has had his reasons to. We here will support him no matter his decision. As I am sure that Rafa has done so what is best for himself & his career.