[DiapDealer]

If it happens again, I would suggest making sure Sigil's entire program directory is exempt from malware scanning. Not just Sigil.exe

Since I suspect the problem is related to Sigil's online update checker, you could try blocking Sigil.exe from accessing the internet entirely (with your firewall). Doing so might actually trick Sigil into thinking there's no internet connection, thus skipping any attempt to contact github.com (to check for the latest version of Sigil) via ssl altogether.

There are several third-party Sigil plugins that check for new versions of themselves in the same manner. So if you use any of them, it could put you in the same boat. But that, at least, would be python.exe making the call and not Sigil.exe.