@danj
Thanks for your advises. Unfortunately I can not transfer them to my Mid 2012 Macbook Pro 15".
Over the last years I had a 128 GB Samsung 840 PRO in my Macbook. Now I wanted to replace it with a 2TB Samsung 860 EVO. With this drive I experienced all the problems described above. So I bought a new cable for my Macbook and this didn't solved the problem at all.
The new cable seemded to be an original Apple-product.
Is there any SATA III cable for a 15" Macbook Pro which works with the 860 EVO?