Jumpy Sticky Behavior

I’m noticing a weird behavior on my sticky elements on my website. They seem to work fine in the designer, but have a jumping, stutter-y effect on the preview and live site. It seems to only be a thing in Safari, from what I can tell—works as intended in Chrome (maybe check it out on Chrome to see what I’m attempting).

My guess is one of my position settings are somehow conflicting with the sticky setting, but I can’t figure out which one.

Any help would be appreciated!

Read-only link here