No that's definately different from what I had... I couldn't even access my router to check arp when it happened to me... Nevermind it turning back to normal, even for a while
Is it perhaps not a issue with 3.18, considering it's been released just a hour ago! make a support output file when it happens again, mail it off to MT, and I guess, try and see if the same happens on 3.17....
You really shouldnt be deploying new versions to production / critical routers within a few minutes of it being released
testing things is king in this business