Why is there a problem with DNS?

Question

Domain Name System

I suddenly discovered that domains ("unknown host") are not pinged from the guest machine, as a result, curl, wget, etc. do not work. At the same time, IP addresses are pinged normally. I did not change any settings, everything worked fine before.
In the machine settings, 2 network adapters are enabled:
1. NAT
2. Host virtual adapter
Reinstalled both Vagrant and Virtualbox, does not help. What could be the problem?