I've had this too, a lot. It seems to happen when there is a layer mask in use. If I zoom in and out of the image the missing area moves around, sometime the whole image is not visible.
I just finished reading that thread and thought well, there’s no need for my thread now, came here to update and post a link, you beat me to it haha, glad to see I’m not missing something obvious, it’s funny how once you know there is only a certain way to achieve what you want it makes the whole thing more bearable.
Here is a good way to get familiar with the comparison. I made this list on my own time, because I thought Photo seemed a lot more compact, so I wanted to become familiar with what Designer has that Photo does not to make the comparison more equal. Many things can be accomplished in both, but the main thing to remember is that Designer is for vector drawings and layout, and Photo is for photo editing.
What’s the same?
Vector Features:
Boolean operations
Converting to curves
Pixel editing on vectors
Clipping and masking vectors
Smart shape presets
Pen tool and pen modes
Gradients on objects
Stroke profiling
Photo Features:
Layer adjustments
Marquee, lasso, and brush selections
Common adjustment tools
Blend modes
Other:
Export persona and slice tool
Bitmap pattern fills
Power Duplicate
Pixel tool
Advanced paragraph formatting
Over 1,000,000% zoom
What’s different?
Only in Designer:
Corner tool
Vector pencil tool
Vector brush tool
Transparency tool
Expanding objects
Vector brush presets
Type on path
Symbols
Assets
Constraints
Only in Photo:
Flood select tool
Color replacement brush tool
Paint mixer brush tool
Advanced eraser tools
Sponge brush tool
Clone brush tool
Undo brush tool
Median brush tool
Inpainting brush tool
Mesh warp tool
Perspective tool
Liquifying tools
Development tools
Tone mapping tools
Etcetera studios