In one of instance sometimes "Temporary failure in name resolution"

Hello all

Have an instance running Ubuntu 18.04 it was working fine but observed sometimes it would simply throw "temporary failure in name resolution" when pinging any domain resulting in error by any app that'll be communicating to specified domain.I manually need to add any DNS like 1.1.1.1 in resolv.conf that resolves, but why the issue happens as faced similar in one of instance earlier as well and other instance in different regions works fine