Material bug , comple bug , performance bug in ue4.20 !!!

hello everyone , i find out a bug in materials in unreal ue4.20 as you can see in those images :;base64

here i just added texture node and compile is more then 400 at start;base64

here i just create simple material and change privew many times

after i lot of tests i finded out this

and i tryed to create project to test if this my problem and its broken just like my project

epic please FIX