I'm not a fan of conspiracy theories, but this very much seems like a scam.

I had an AC discount code to use (the type you get as compensation etc.).

I'd previously priced an itinerary in N class (round-trip with one stopover; AC flights only) and got a decent price. When trying to book the itinerary a few minutes later using the discount code, to my complete surprise, the whole itinerary priced in E class. The discount code was applied, but the total cost was more than double, so completely useless.

I figured availability may've changed, so I checked both Expertflyer (which showed plenty of N availability) and tried again pricing the itinerary with and without the discount code. About ten times. Each and every time it priced in N class without using the discount code and in E class with the discount code.

Thinking this is absolutely ridiculous, I decided to call AC and ended up spending 2h on the phone with AC - which was a complete waste of time. After getting past the "availability changes constantly", "your promo code may not be eligible for N class" (other itineraries in N class priced fine), "there's N availability, but you're not meeting the advance purchase requirement" (nonsense), I finally got an agent who realized I wasn't completely stupid, but despite working with the resource desk, was unable to resolve the issue.

After 2h I figured it was time to call it quits, but I'm still wondering:

Does AC arbitrarily block certain fares or availability in lower booking classes based on whether a discount code is used or not? (I've obviously seen regular "promo codes" that were only valid for Flex fares or higher etc., but if this happens with a discount code without any (published) restrictions it does seem like a scam.

Has anyone experienced something similar, and more importantly, is there a way to resolve this with AC?