Imp definitely stacks and says so. That's actually the problem. You have 2 resistance, it adds 2 to it. RAW the wording on imp screws it up if you have Akanul.
The problem with the interpretation is that the Imp's bonus in the game that explicitly stacks with other bonuses to become worse than if it didn't stack with another bonus.
The general rule is that when non-stacking bonuses apply, then the better one applies. In this case the bonuses explicitly stack. Surely having 2 bonuses that are designed to stack can't be worse than having 2 bonuses that don't stack.
The thing is, RAW isn't really written. It's an interpretation and guess. There is no rule written that says a background bonus is applied before a level 1 feat bonus is.
Types of bonuses and values of bonuses matter, order never has anywhere else. Saying that logically a background comes before a feat is inferring rules that are grounded in fluff, not mechanics.
Unfortunately, there isn’t an official answer for the situation you describe. I’ve passed along this conversation to the game’s developers. Hopefully, we’ll see an update or FAQ entry covering it soon, but until then it’s up to the campaign’s Dungeon Master to decide. The DM is always the final arbiter on how they want their campaign to run. Have fun!
Please let me know if you need anymore help!
Charles
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Using the CB and following the built in sequence (not manually jumping back and forth) with the next button, backgrounds appear first so it's 2+2. And RAW would support that in my opinion.

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Rulebook featuring "high magic" options, including a host of new spells.