The thing about the repayable levels is that the the gem counter only adds the number of gems greater than the ones you already received playing the level. For example, say you got three hundred gems by beating Backwoods Brawl, level 0. If you beat it again, and it says you get five hundred gems, you would only receive two hundred.
For more information, go here: Incorrect Gem Awarding on defeating Backwoods Brawl multiple times