Does turning off »Use Graphics Processor« in the Performance Preferences (Photoshop > Preferences > Performance > Graphic Processor Settings) and restarting Photoshop have any bearing on the issue?
You may want to add your »Mea too« here:
https://feedback.photoshop.com/photoshop_family/topics/photoshop-19-1-in-fullscreen-mode-c anvas-moves-to-upper-left-corner-and-3-4-of-the-canvas-is-unusable?utm_source=notification &utm_medium=email&utm_campaign=new_comment&utm_content=reply_button&reply%5Bid%5D=19277210 #reply_19277210
And please try whether the work-around of hitting tab twice works for you.
This worked! Thank you so much. Is it good to not use the Graphic Processor? I've never had to uncheck that before. Thanks! I'm going to check that link now.
Is it good to not use the Graphic Processor?
Not really, certain features (Rotate View Tool for example) depend on it, others benefit from it (some Filters can run faster).