Mysteriously Lost HTTPS Access

Hi friends,

I have been ruing a 14.04 server since it was first released in April 2014. I run several web applications/sites, the most important of which is ownCloud. In summer 2015, after ruing fine for over a year, HTTPS mysteriously stopped working.

HTTP access continues to work. I have not changed ISPs or changed any router settings. I do not believe that I did anything immediately prior to HTTPS breaking to cause it. The server has been kept up to date with patches, but hasn't otherwise been used.

Can anyone recommend how to start troubleshooting this?

Thanks!