DiDa has already helped me with this via PM and I'm making this post as a curtesy from his request to do it. This is a 2 in 1 in that I had 2 issues with the Dungeon Hunter 4 IPA Mod and both were resolved.
When you Install the Mod with Impactor sometimes the game may glitch and give a negative amount in gems resulting in not being able to purchase all the "gem" priced items in the game. This is fixed by doing another install of the game through impactor again and it should work fine eventually.
Second issue is related to the first, the game has no built-in backup for your save data. This means that when the 7 day period ends for the IPA, do NOT uninstall the app, just use impactor to install the IPA again over the original install. This will keep the app on your device and maintain your data.