I bought a mature 18 ft Purple Fountain Weeping Beech last year from a local nursery, planted it late February 2020.

The top 1/3 lost leaves last summer and I put a 20 gallon water bag under the tree from June to September.  

I noticed the top 1/3 did not leave out this spring. I began to trim the top and noticed the limbs were dead. Scratched part of the main trunk until I found where the green/live part ended and trimmed to that point. The base of the trunk and has noticeable cracking and bark that can be pulled off. It looks like there is a white fungus/growth around some of the bark. Is this caused by a disease? Should I let it be or completely remove it? I have a Tri Color Beech about 19 ft to the left of it. I am worried if it is a disease it may affect my Tri Color.  

Any help would be much appreciated.

It appeared to thrive last spring and has progressively declined. I have included photos from today.