How to find the cause of mikrotik dns internet failure?

Question

Computer networks

Hello.
There is a network built on mikrotik hex S. It, in turn, takes the Internet from the Eltex NTU 1421G provider's GPON router.
On Eltex, I fixed a static ip for Mikrotik and made dmz on the Mikrotik ip, so as not to forward ports twice.
On Mikrotik I made a network different from Eltex (on Eltex 192.168.1.x on Mikrotik 192.168.13.x)
Mikrotik distributes Yandex 77.88.8.8 dhcp dns 77.88.8.8 Mikrotik
is connected to a Fibertool FT-AIR-DUO-G router in access point mode.

And the problem is that if no one is at home for a long time, then Wifi users lose access to the Internet. There is a suspicion that there are problems with dns, since it was empirically discovered that the tracert command from a smartphone treats 7 out of 10 cases.
I rarely noticed this on a computer. The computer is wired to Mikrotik.

What to do? The output of which commands to provide for the concept of what's the matter?

Answer 1

I've been seeing problems with Yandex DNS for half a year now. Contacted their tech support, there is a ticket from me with a description of the problems that they are considering, but so far there have been no answers.
I can advise you to make MikroTIK itself a DNS server, and specify either the provider's DNS or DNS from CloudFlare as the DNS on the router, or better, both. So it will be more stable and faster.
PS
And yes, increase the lease time in the DHCP settings on MikroTIK to 12 hours.