Hi!
Excuse me, but I do not speak enough English, so I had to resort to the assistance of an interpreter ...

Starting with version 4 and 4.6 there is a problem with the server DNS, which is as follows ...
About once a day DNS service stops responding. At the same time - completely, as well as the wasted opportunity to view / change anything in the IP-> DNS (there's just empty). Helps only reboot.
But the problem with reboot router in that it serves about 700 users ...

Please, help!!!

I had this problem too, it happens randomly, to resolve I put 2 servers running ubuntu + dns bind9 and the PPPoE server profile put the ips of the servers in the DNS, solved my problem .... I had to abandon completely the mikrotik dns server .... Goodbye.

Mikrotik states in email to me that 4.8 has improvements to DNS although not listed in the changelog.
Id try this.

But please report back, you have crashing more than me, and want to know if 4.8 fixes your problem

Thanks!