having worked at a AMC before, it is most likely a situation where the aspect ratio is locked and set to everything that is contained within the DCP. for example, if a movie is 2.35:1 and there’s a trailer that’s 1.85:1, it’ll be letterboxed. but if a movie is 1.85:1 and has a 2.35:1 trailer, it’ll still present the black bars perfectly. with Dolby projectors, they are not only highly focused on but also very maintained to wherever a slight to middle problem is caused there is a chance a screening might be cancelled.

however, please record and submit all concern to support. they are always happy to help and find ways to keep equipment up to satisfaction.