Upon further investigation it appears that using the non-SSL version of instapaper.com causes no issues at all. The script works as it did in 6.35.
However if I switch the URL/Port to use the SSL version of the API, I experience the hangs and/or forcibly closed connections.
Issuing the following command (after clearing mIRC's SSL cert cache):
/sockopen -e testSock www.instapaper.com
gives me a prompt to accept the certificate (which I do, permanently).
From here you can close the socket /sockclose testSock.
Repeating the process will get me prompted another two times (for a total of 3 certificates).
I assume this is a result of a server-farm of sorts on the website end of things. However I don't recall this behavior in 6.35. Following me accepting all three certs. I still have issues where the website only responds in a timely manner once every few times, whereas the non SSL URL responds immediately.
I'm honestly not quite sure whether this is a result of the update to mIRC or a bad coincidence with that website, but I'm not sure how else to trouble shoot.
I feel that calling this a "bug" is probably not totally correct as I can't replicate it on command. I will post code as soon as I can make it happen every time; but in the mean time suffice to say even when it works via SSL, the time to achieve it is substantially slower than both non-SSL, and my using SSL on 6.35.