I believe this is the exact issue I am experiencing on 5.0 Beta 2. It got ALOT worse on 5.0 B2. I had hardly noticed it on 4.6-4.9 but on 5.0B2 it fails at most in 1 hour or less.. With the watchdog turned off it hangs the router but does recover by itself after some period of time.
This is on a 450G. My power supply is doing 14.6Vdc and has 3 amps available.
Im using a Mikrotik image for the meta router.
I have a thread on this at http://forum.mikrotik.com/t/450g-5-0-beta1-issue/37215/12 and have sent support requests.
My watchdog timer does not generate autosup for these events..