Digital Foundry addressed this in their campaign review and it seems it was an intentional design decision (maybe to optimize the game?). They really called upon 343 to review this decision and fix it (also affects cutscenes).
I’ve noticed it particularly in BTB where the frames drop even further and made a clip to send to Halo Support. I filled out all of the required fields (including platform) and received a reply to update my drivers and a link to a PC article. I use an Xbox One X…which makes me wonder how useful the support tickets actually are…
Have others noticed the slideshow animations? Has it negatively impacted your experience playing the game?