I had a quick look over the site but couldn’t find anything obvious… I also checked out the published version of your site on my 4k monitor and saw nothing odd with the layout at all there.
I note the magnifying glass with a - symbol in the browser tab though. This could just be a user error. In Chrome at least, when you alter a zoom level on a site it will remember it and use that going forward for that site only.
User zooming out looks like the most sensible problem right now.