We get the same on one (busy) site, so much that I made the other ISP the primary.  The issue still persists, though perhaps a little less frequently.  Having seen this I'll log it with support as both ISPs cannot see an issue and the users don't either.   Funniest thing is that they are both MPLS links and the default routes are on the same stack at our main DC and from there they both go through the same internet firewall, even on the same rule, so not sure how one is down when the other is up...! ... View more