When going through the dungeon, I will have collected some amount of gold, but when I return from the dungeon, my gold will be the same as before I went through the dungeon. The first time this happened, I decided to try again to verify that it wasn't my own error and have not received the gold increase expected for travel through the dungeon.
AT&T iPhone 6S Plus running iOS 9.0.2
Ok first off, please check to see if you are using the merchant class. The merchant spends gold to use his attacks, so there's a chance he's eating up some of your gold.
Second- the banker has limits in place in terms of how much he can earn you at a given time, based on how much you left the game with.