Getting browser security warnings on this site

When I open this discussion page, I’m presented with warnings that the site is unsafe. If I bypass these warnings and proceed anyway, I get the “Not secure” warning in the address bar with the following details:

Your connection to this site is not fully secure

This site uses an outdated security configuration,
which may expose your information (for example,
passwords or credit card numbers) when it is sent
to the site.

Can someone please check into this situation? This appears to be intermittent, which suggests that one or more of the machine in a load-balanced cluster haven’t been updated, while others have.