When was this?
I experienced this glitch in 2020 (after parks reopened) when the “Resort Guest with AP” category was not a choice and I had to use the AP category. A park was unavailable for AP holders, but the resort concierge was able to switch my reservation for the park I wanted.
They knew at the time it was an unfair situation for resort guests with APs.
Soon afterward APs had the two options to choose from and over many visits the (nearly) last three years, I have never not gotten the parks I want on the days I want. I do book in advance during busy times (just I visited Easter week.)
That’s why I believe “Resort Guests with AP” do not share the same bucket as APs, but likely share with “Resort Guests with Tickets.”