Do you have any specific node examples or scenarios that can be tested/repro'd?

Ah! Ha-ha-ha!!! Oh, heh. Haha, ha... oh, oh, you! ++ for the power of positive thinking and following up on help desk requests.

$ curl -I http://perlmonks.org/?node=Recently+Active+Threads 2>/dev/nu
+ll | egrep -i 'date|cache|modified'
Date: Mon, 12 Oct 2015 21:43:54 GMT
$ curl -I http://perlmonks.org/?node=Recently+Active+Threads 2>/dev/nu
+ll | egrep -i 'date|cache|modified'
Date: Mon, 12 Oct 2015 21:43:57 GMT
$ curl -I http://perlmonks.org/?node=Newest+Nodes 2>/dev/null | egrep 
+-i 'date|cache|modified'
Date: Mon, 12 Oct 2015 21:44:07 GMT
$ curl -I http://perlmonks.org/?node=Newest+Nodes 2>/dev/null | egrep 
+-i 'date|cache|modified'
Date: Mon, 12 Oct 2015 21:44:09 GMT
[download]

At least I didn't ask "did you turn it off and back on again?" :)

I lately observe that the content is often many days(!) out-of-date ... until I log in...

I don't know if the problem is on your end, or somewhere in between, but it's not on our end, because PM doesn't cache any output. (There are a few pages which are "cached", such as Selected Best Nodes, but you don't seem to be talking about any of those.)

If you would like to take some screen shots the next time you see it happen, and send them to me, I'd be happy to take a look.