I am having several very frustrating issues with the Character Tool in Photoshop CC 2018 Rel. 19.0.1 (latest) on both Windows 8.1 and Windows 10.
In Windows 8.1, many of the fonts do not render a preview but instead render box characters. Didn't used to be this way...
In Windows 10, all of the font previews jump back and forth (left-to-right) as you hover over the fonts in the list.
Furthermore, and most infuriatingly, if you hover over a font that is also displayed in the quick list at the top, the hover-indicator JUMPS all the way back up to the top of the list, forcibly scrolling the list all the way back up.