Is anyone else having problems retaining dimensions in video carousels?

TL;DR: I used to be able to retain the same dimension for videos across a carousel. Today, though, Instagram started automatically changing the dimensions of my videos to a portrait-esque vertical dimension (making them super zoomed-in in the process), and the "fit" tool doesn't seem to be working. Has anyone else noticed this sudden issue or am I the only one experiencing it?

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So, in the past, I have always been able to make carousels of 60-second videos -- with each (video) slide retaining the same dimensions.

However, today, I tried making a carousel containing multiple videos like I always do -- and something different (and unfortunate) is happening. I'm able to set my specified dimensions with the first video using the "fit" feature; BUT, when I try adding a second video (and third, fourth, etc.) to the carousel, the newer additions are AUTOMATICALLY cropped to a portrait/vertical dimension. (Even if they already share the same dimension as the first video.) In other words...

I'll make slide one a standard horizontal video. Then, I'll select the "fit" tool so that the following additions to the carousel retain the first video's dimensions -- just in case. Next, I'll add another video (one that literally shares the dimensions of the first video, and is horizontal)... yet Instagram immediately snaps it to a vertical dimension. So, when you finally post, the following videos are super zoomed in.

(Other times, when I go in and try to add multiple videos to a carousel, Video #2 (per se) gets snapped into a vertical (zoomed in) dimension; and sometimes, the same thing will happen to the first video!)

I know a third-party editing app may help me going forward -- that helps you resize videos to fit into carousels, helpful before Instagram added the "fitting" tool -- but I don't feel I should have to start doing that again. Plus, I noticed that my overall video quality decreased significantly when I made a carousel consisting of third-party edited videos.

Is this a glitch for Instagram? Because this has never happened to me before. Is anyone else experiencing the issue too?

EDIT: 5/6/22 When I try to post a single video (or a carousel of them) -- the thumbnail selection seems to be slightly different now. Now, when I have the option to pick the thumbnail, it only shows me a portrait dimension preview. It's almost as if Instagram is passively-aggressively trying to force people into their Reel concept and discourage traditional "60-second horizontal video" posts.

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The first video that has been selected for the carousel is obviously horizontal, as can be seen.

This second video is actually ALSO horizontal (rectangular), but Instagram is instantly snapping it into this vertical/portrait dimension. Sometimes, this will even change the first slide too, and all the other slides.