Ssl Error Only on Certain Sites

I'm on Windows 10 and getting an ERR_SSL_PROTOCOL_ERROR on some sites that use SSL, but not others. For example, uses SSL and the site works fine, but and do not work and I get the SSL error

This doesnt seem to be an issue with their server because 1) a number of SSL sites dont work and 2) all sites work when I try using my laptop

This is also not an issue with Chrome, because I get the same SSL error when attempting with Firefox

I've attempted the usual things like restarting my computer/router/switch/modem, and I've even cleared my browser cache, my SSL state cache, flushed windows DNS cache, and flushed chrome DNS cache (as per the answer here: Chrome ERR_SSL_PROTOCOL_ERROR on known working site)

Any thoughts on why I'm getting this error only with certain sites, and only on this particular computer?

EDIT with additional information:

• I'm not using a proxy on this computer. My server used to have privoxy set up but 1) it has since been turned off and 2) my desktop computer was never using that proxy to begin with