This also occurs on the Projects pages, News, and About pages, but not the Home page…
The first thing I noticed is that the “Recent Projects / Featured Work” page is build differently than the homepage, most notably on the left side border element—where the former is using a 1px wide div in a fixed position 7vw from the edge, while the latter is using a 7vw wide div in a fixed position against the edge. That makes me think there are a bunch of other differences that can attribute to the over-extended horizontal lines, but ultimately I am curious why you ended up building the layout this way instead using the “blocks” down the center to define the borders?
Typically the more complex you make your layouts the more opportunities there are for issues to come up—especially across different browsers. This layout is actually very simple when you break it down, and can be recreated with center-aligned containers with a left, right, and bottom border (shown in the gif below with different colors):
With this structure, your center containers don’t need to rely on the left and right containers to line up—instead creating the vertical borders with their own edges.
If you have the time, I’d suggest making some changes to mimic what I’ve suggested above (at the very least, on a test page) and see if it doesn’t help solve your issue. If you prefer to stick with the structure you’ve already created, I’d make sure you copy the layout and element styles from the homepage as it seems like it’s working as expected across all the breakpoints.
Feel free to reach out if you run into any issues or have questions