Q.Bacchus Noir Black Mulberry Tree
This is about the 3rd year I have had it. It really just started to grow and flourish this spring. It’s about 3 to 4 ft tall. Now all of a sudden all the top leaves are missing. The bottom of the tree appears healthy and still has its leaves. I have other fruit trees that are fine. I had considered deer but we live on 42 acres with plenty of other trees for them to eat and since none of my other fruit tree leaves are affected, I dismissed that thought. The pic attached was just taken today, and I see the branches have some new growth. Was I wrong about the Deer? Any suggestions?

lol yea, as I said in my post the "new leaves" are just growing back. That was a full bush until the leaves just vanished at the top. My question was " what could have happened to the leaves"?
Also it unbelievably has rained here almost "every" single day for the last 3 weeks, except for today. So it has had plenty of water. I hadn't been able to cut grass in over 2 weeks because of the rain. And when you say "fairly new planting" you did read where I said it has been planted for 3 years right? Also as I said it was growing good finally, until the leaves vanished so it must be getting enough sun too.

It appears that the tree is growing quite slowly, the leaves look like they are just emerging.
Your image does appear to have quite a bit of shade in it.
Full sun would be preferred, but they can grow in partial shade.
Mulberry Trees do not like to be dry. They like a damp soil and it may need some watering due to it's fairly new planting.
You could add 2 to 3 inches of hardwood mulch to help the moisture from evaporating.