I've been getting unsafe ssl errors when trying to browse imgur. How can this be?

I’ve been getting the error whenever I click on an image link on reddit.

Res cannot display images ( here is an example )

I get this page as an error when I click on the imgur link directly.

When I examine the certificate I see this. It seems ok? I dont know…

I’ve narrowed down the problem to the wifi im using at work. Whenever I tether my connection from my cellphone it redirects ok and I get no error what so ever.

So my question is: whats been done to the router that causes this? I’ve admin access and can fix this issue if its on the router but I dont know whats wrong in the first place. Could someone be showing themselves as a dns server and doing a man-in-the-middle attack?

I have some knowledge about how ssl works but I might not be correct in that regard.