I just remembered a theory that came out during the SHs reunion on SA=
The two guys in suits that kidnapped Cocoa (Fake-Robin) were from the Revolutionary Army that was after her. Basically, the theory was that the Rev. Army didn't way to let her go so she escaped them to return to the crew, so now they were after her to bring her back to Baltigo.
This was shot down several times but would still come up due to = "hey no evidence!" (for either side).
But thanks to Dressrosa Arc, we do have evidence. IF Robin left on bad terms, then Koala, Sabo & Hack wouldn't have been so laid-back. Even if say "oh but they likely helped her escape!" then they would have made a comment during their reunion, but no…