First, I am not sure if this is it, but if you start a new character in Bloodtrail, everything resets, so you lose your city and can't access it until completing the story again. If this isn't the reason, then it is probably either that the game isn't saving character information to the correct location (if in single player) or the correct server isn't syncing your data (if in multiplayer). I am not sure how the server work, but it might be possible that each server saves its own city and character data so if you start connecting to different servers it might cause that (or at least a delay in saving the data).