That is a bit odd. It is either the ISP or a problem with the router,
of course.
First thing is to make sure the router firmware is up to date.
After that, you might try swapping out with a different router or
calling Linksys to see if it is a known common problem, and hopefully
has an easy fix.
Hope this helps.
Kind Regards,
Bill Krahmer
Internet/network service monitoring software.
"First Alert Service Monitor" - Free trial.
http://www.electrasoft.com/fasm.htm