Microsoft mistreated a security researcher, the researcher publicly dumped a horde of Microsoft zero days, Microsoft was decidedly miffed, the researcher says they'll "shatter Microsoft's bones" on July 14.
The certificate was issued before the Nightmare Eclipse zero day thing started but I suppose it’s possible there are other certificates expiring around the same time that could be connected to the Nightmare deadline. Probably a coincidence though
It’s also the day before SharePoint 2016 and SharePoint 2019 (both considered office products) fall out of support and have to be replaced by SharePoint subscription edition.