Let's cover two but lead with clicking no was IMO the right choice.
Any cloud app could have this happen. Causes? Your date and time might be off or the site certs expired and they renewed them.
Thousands of security alerts keep popping up on my computer... It says its due to a website but I had no websites open over the weekend when this happened. The only programs that I had open were Photoshop CC, After Effects CC, Premiere Pro CC, and the Creative Cloud App updater... I ran windows defender to see if something popped up on that but got nothing. What do? This has happened before but instead of looking into it I just spam clicked them all away with the "no" option and all was good..
edit: Forgot to mention when I click "View Certificate" nothing shows up..

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic