Solved the problem. Got my wife a Galaxy S7 last week. She was having a heck of a time with Facebook and her phone was old.
Got the new one at Costco and got a $250 gift card with it.
Got rid of mdnsd problem for a couple days by removing weather apps but now it's back and Facebook is not running correctly and mdnsd is back again. So I agree whatever the problem is that Facebook may be a culprit too. Interesting problem for sure.