Not sure if this data point will muddy the thread, but I constantly have the same issue with looking for award redemptions. Once I check the "use points/awards" in the search box, then it'll show rates unavailable as if I used a bad corporate code.

One fix I had, and this should work for you too, OP, is to use the mobile app. Mobile app lets you use 5 corp codes at the same time (award redemptions inclusive of that) and it will show you the lowest rate for the code eligible. It'll point out whether the price is for the AAA code, another XYZ corp code, or ABC code, or the lowest regular rate. Click through to select with corp code you want for a slightly higher cost.

Back to my problem, though, this means that I'm just exclusively booking on the app because it shows my search results, with how many points the stay will cost, as expected! It simply doesn't work on the browser!!