@ArMouReR Strange behavior, it looks looks like more SSD related than NUC. Did you install WIN7 directly or by putting an image on SSD? What type of filesystem are you using? NTFS?
If I were you I jsut only re-install WIN7, reformat the unit and see how it goes. If you have a spare SSD unit well...it should be easier to troubleshoot.
1. It was clean install
I do have spare SSD - Sandisk ultra 128Gb. I want to clone the system on this drive and check.
But it will take time - I can't put this system off. Other then restart there is no other issues - everything works fine.