It's possible your ISP is using some type of caching system that went hay wire for a bit (or something local to your machine).
I run behind a squid cache quite a bit and have seen things like that happen from time to time. I'm not technically minded enough to understand it all but usually a reset of the system on the ISP side solves it. I would assume your provider or you had some sort of cache delivery going haywire.
As an aside...DEXTER went through a quick reset a few hours before you reported this issue but the two would have no relation whatsoever with each other.
It's really hard to say what happened on your end but obviously something went awry and fortunately whatever it was appears to be fixed