Okay, here is some information that I think you'll find useful:
The Game Center account FIRST used to login to the game will be used forever, for patch 1.0.0 and 1.0.2. We are working on ability to switch accounts.
Gold/story rewards/purchases/chests/collection cards should be synced between both devices, as long as they are the same account.
This means if you completed Brigandoom and/or Poison Pill on iPad A, you will not be rewarded for it on iPad B. This is due to it being the same account and trying to reduce farming.
If you want to essentially earn gold for repeating content, this is where Quest Mode would come in handy, which we just patched and made much more stable.
Experienced characters should be LOCAL only. Same with actual save game progression. For example, you may have completed Brigandoom and Poison Pill on device A, so you won't be rewarded on device B if you do it again, but that progression will not transfer.
Save game syncing is something we are working on, so have no fear! We know it's a demanded feature!
Generally, the best fix for most solutions, is shutting the app down entirely (clearing it from recently used apps) and relaunching it. It'll resync all your data, especially when working with the same account on two devices.
The "sometimes this syncs, sometime this doesn't" aspect of your problem is troublesome, so I have notified our QA team and we're trying to get repro steps on it.
I hope I helped! If you have any more questions or concerns, ask away! d(^_^)b
And thank you for playing the game and being patient with us. Also your report and steps at which you specified how to reproduce it is splendid! :D
leProgrammer's post in Two iPads, Family Account, Bundle Purchase, One iPad no gold was marked as the answer