Subsequent connections to websites are failing on entire network

Starting late last Friday, internet at our office stopped working and attempts to remotely connect would fail.

Internet remained down until Monday morning when I restarted our firewall (which seemingly did nothing) followed by our network switch, which appeared to resolve the issue. I'd like to note that I was able to successfully ping google.com between resetting the firewall and switch yet webpages were not loading in a browser.

By 11am on Tuesday, the internet became extremely slow or nonexistant and still remains this way. Our ISP saw nothing wrong from their end.

Usually the initial connection to a website will load fine, however further navigation on that website will initially stall for 20-30 seconds before maybe loading (very slowly) or more likely an error such as "ERR_CONNECTION_RESET".

The issue is very noticeable in our ERP (NetSuite). If I close and open Chrome, I can go to any URL in NetSuite and it will load fast as usual. Navigating to another page is when the page stalls (according to Chrome Dev Network Tools) for 20-30 seconds and usually won't load. Restarting Chrome lets me access the new page near instantly.

When going to fast.com or speedtest.net, we see the usual ~50Mbps download speeds. Upload speeds on speedtest.net have been <0.10Mbps, however that may be due to our firewall.

Does this sound like hardware starting to die, or something else?