I only have a test site for now, if this should not be posted publicly, please remove.

I uploaded a few images to the gallery, they uploaded fine.

https://squarewheelscycling.com/test/index.php?/gallery/

I can't scroll down the page, and if I hover over an image, it bounces.

Everything seems to work OK for me. I can scroll down and no bouncing images. When I hover over a image it just zooms in a little. 

Works fine for me.

seems fine to me as well

Hmm, Win 7, Google Chrome I get this:

IE 11 worked fine.  This is my work PC, so it's still on Win 7.

Confirmed (with Chrome and Edge at least). You just need to collapse the browser width to less than 1300px to get it to break. Do that, or even less wide, and now look at how the images set up and try to scroll down the page.

There is a hell of a js controller attached to the image tables in Gallery and what you are seeing is that controller not working correctly (image thumbnails spread out past row width into body elements, unable to scroll down the page without it immediately popping back to the top, throbbing elements, etc.). I submitted a bug report regarding it during the beta (and eons past too) but to fix it is some kind of work. I'm assuming something was done to it but appears still messy. I imagine Rikki is rocking back and forth and muttering to himself at the prospect of looking at this controller again.

The problem is in how the controller wants to collapse the image table as you shrink the browser. It wants to stick as many images as will fit at the correct aspect ratio per row. Once there isn't enough room it will either resize the images in the row to get them to fit, or once it hits a certain limit, will remove/add an image to the row. When the browser is wide, past that 1320px max-width (or whatever that number is) the controller is all set and happy. But as you collapse the browser width, it's losing the certainty it has to have and freaks out. I have some thoughts on fixes but its a messy messy job.