My late IMAC 2012 i7 fusion gtx 680 crucial experience has been awful. I used the tool on their website to determine which ram i need to use. I kept the stock 8 gigs and added the 16. Ever since I've put it in my computer has not run smooth. Won't wake up or start half the time. Randomly turns on at 5 in the morning after pushing the power button 8 hours earlier. I've tried every combination with just the crucial ram in and it still gives me issues. Now I'm currently just using the stock 8 gigs and have 16 gigs of ram sitting here.
Time to figure out how this return process works and if they will refund me.
THAT does not sound like a memory issue.
You need to get your new iMac to a priest and have an exorcism.
When you say that you've "tried every combination" . . . do you get dysfunctional behavior with only the Apple/Hynix memory installed? If so, return your iMac.
If the dysfunctional behavior is only evident when the Crucial memory is installed . . . you need to contact Crucial and have them replace their failed memory.
[EDIT]
It is possible that the factory memory is also failed. You need to troubleshoot to diagnostic standards so that you know what you have and address the issue with Crucial and/or Apple.
[/EDIT]
I installed 2 x 16GB Crucial kits (P/N CT3650282) before my iMac ever saw the power cord. It runs like a hungry Cheetah.
(these 16GB kits must be popular, Crucial has raised the price over $35 USD since I purchased in early Dec)