Hmm, not sure if you should steep now!
I say that because, NO, my TFA Cheesecake Plain smells fine in the bottle, maybe strong buttery smell w/ a little vanilla. A bit less rich smelling than Bavarian Cream, with a bit more butter like smell to it. Similar to LA NY Cheesecake, but that one does have a little bit of a sour cream or cream cheese smell to it (But it's good kind of cheese smell
). None of them smell rancid, or like bad cheese, butter, or milk ect.
So I do think you might have a bad batch!! Hard to say for sure because we can't smell each others to compare... Man, that sounded bad haha, here, smell this!
But ya, it does sound like the batch you have might be bad! I'd go ahead and contact the vendor for a replacement, especially if you purchased it recently. I don't know if it can spoil, how long that would take, or how it would smell when spoiled, but it sounds like yours might be since you mentioned rancid.
For your reference, my batch is - TFA-131510 (From WL)
Great to hear your toffee turned out nicely! I need to order some toffee and caramel flavors myself, thanks for the reminder!