I read all topics about this problem and tried all solutions. Some helped but only in specific scenarios they are no options for me. There was not mentioned (at least for me) REAL cause of this error so I am creating new topic. I hope it is more helpful...
All proposed default Ps workspaces have tools panels docked to left margin of screen. It is why they let you to open files in normal size. When you dock your Tools panel to right margin of screen all is okey too. Any panel, however docked or not to any other or margin does not make difference. All works still good. Problem occurs only when you undock your Tools panel from left/right margin of screen. If you move it few centimeters from left margin all is still fine, but always when you move it farer to right side of screen (and from up) an created/opened document will minimalize its size due to Tools panel distance from left screen margin. If additionally you dock your Tools panel to any other panel that is not docked to left/right margin of screen (but moved to specific location in your Ps workspace) error is going to occur while creating/opening document.
This is of course bug! The only I can do is to turn off Tools panel what is ridicolous solution or else dock it to right Ps screen margin what doesn't satisfy me too for reason It covers too much space along with other panels I keep as small as possible.
This is my first day with CC 19.1. So far i used CS6 for few years. From that I read prior CC versions doesn't have this bug yet.
Since I use specific panels location I can't work with this bug. I'm going to use CS6 until next CC update that fix this problem.
That's really funny first action, opening file I did in newest Ps after relocating panels (including Tools) ended up with error 🙂