Asterisk getting stuck for 10 sec every minute

I am running Asterisk 11.8.1

I have 150 concurrent call in pick hour. and it was ok.

recently my users complained they cannot make call on first attempt most of the time. I have run through may thing. and identified that asterisk doesn’t replay to any invite for at least 10 seconds every minute.

even the console show nothing on this period.
I don’t know what could be the problem.

I have changed the qualify frequency from 60 sec to 300 sec. nothing changed.

any help??

Check your DNS settings