I have a bad bug / problem in Photoshop cc 19.xx. (all 2018 PS Versions) with the adjustment layers.
When I add a new adjustment layer like levels or curves etc., I cant see any changes, that I have done. Also when I switching the layer adjustments off and on, nothing happens. Only when I’m zooming in or out, I can see my results of the adjustments.
I uploaded a video: https://www.dropbox.com/s/s0p1xrfarozv99w/ps_bug.mov?dl=0
Now, I have downgraded to Photoshop 2017.1.3 and its fine and all is working fine. Its only in Photoshop 2018.
I’m working on an Mac Mini (late 2014) with 16 GB Ram.
Try resetting your Photoshop CC2018 Preferences, which you can do under the General tab in Photoshop Preferences.