My first thought here is to map a drive letter to the server and see if that solves the problem.
Since the LR Import dialog window is seeing the drive and the folder and that all the images contained on that drive and in that folder are Grayed Out that means those images are already IN the LR Catalog file.
If you moved those images from where they were originally located, stored, when you originally imported them then you use either the File Missing Files option or the Update Folder Location option to point LR to where they are now located.
Just make my question more precise.
Everything worked fine before the update to LR 2015.8, so the problem came after the update.
Also, some pictures from the folder has already been imported but not all. So I wanted to import the renaming pictures. So when LR starts reading the NAS folder it looks like below, and you can see the LR can see, what is and what is not imported while LR is reading the folder. But when LR is done reading all the pictures it switches all pictures (imported/not imported) to grayed out like screenshot in my first post, and I can do nothing.