I was using firefox on a new mac. Some extensions like ublock installed. I just tried again now with a different browser (latest vivaldi, no extensions) and it behaves the same (search bar, but only if you have "collection images" highlighted, enter key works as expected if you have "all" highlighted). I am still experiencing the slowness and image "popping" when using the show more link. I'm still getting 3 layers of scroll bars on the image viewer. The back button is a little bit better but of course since it's some psuedo-infinite-scroll when I click back I'm landed back at the top of the list with all my "show more" clicks undone (so lost where I was in the results list as is common with infinite-scroll and SPA).
I can't dispute possibility of network issues, could be the site is being slammed, but speedtest.net says my connection is >300Mbps.