https subdomains hang all browsers

If I try to access subdomains like apod.nasa.gov or ordbok.uib.no with the https:// prefix, all browsers on my Win 10 (1903) & 7 SE hang on my ASUS laptop or tower system with TLS security timeouts, but accessing the parent domains with https:// works fine. The router is a Cisco/Linksys E1200, no proxy. Where & how can I troubleshoot this? It's maddeningly intermittent. All other Web access seems to work fine.

Thanks for the response, bro67. Well, I have a laptop connected via wireless to the same router, also running Win 10 1903, and accessing the https:// subdomains works there; it's the Ethernet-connected tower where they TLS timeout, so the problem isn't the router, it's the tower's network settings. Its NIC is a Realtec PCIe GBE family controller. I know how & where to set networking, but not what to set so that it works as it does on my laptop.