This is an odd scaling problem. I have a new fairly 43" 4K display and have it customised to display enlarged text and apps between 200 and 250%. The problem is sometimes after start up I'm presented with super fuzzy text and menus (icons are fine). To resolve this I have to move the 'Change the size of text, apps, and other items' slider to another size and then log out and back in. This always fixes the problem but its damned annoying.