Save for Web issue

[Kate6C14]

This is what my screen looks like whenever I press Save to Web Legacy. Does anyone know whats going on here?

Thanks

[c.pfaffenbichler]

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? 

Does turning on »Deactivate Native Canvas« (Photoshop > Preferences > Technology Previews) and restarting Photoshop have any bearing on the issue?