A request for a domain name goes to the Internet instead of searching in loc.Net

[SektorCT]

Hi all.
What is the problem, there is a domain name server in the local network. There are port forwarding rules. And it seems like the request should remain in the local network, and if not found, then go to the Internet. But sometimes (I can't understand why) the request or ping remains in the network, and sometimes goes to the Internet.
I appeal to those who know this topic, help me understand what the problem is.
Below I attach screenshots of all the settings that are available.