If you have a color fill layer and try to export using "Quick Export As PNG" or "Export As...", a really strange bug happens. It seems like the mask on the color fill layer affects the dimensions of the exported image.
Take a look at the examples below. "Save for Web" works fine.
This is what happened when I tried to export my artwork.
I then removed the mask on the color fill layer. Now it works!
I then tried to see what happened if I changed the dimensions of the mask.
That is pretty wacky... and a bug I think I've encountered before. One question: If you save in that messed up state, close Photoshop, re-open Photoshop, and then do a quick export, what output do you get?
When I use the Export-As and am changing canvas, image, and crops sizes, sometimes the exporter (Generator) loses its mind and a restart will fix it.
Still a bug. Just curious if that is the root of the problem.
Sorry for the delayed response. This is partially due to how generator was originally designed (see this link). Export As leverages the generator plug-in. We are investigating a fix that makes sense given all the various types of workflows.
I was a little confused trying to reproduce your issue at first because I wasn't able to resize the mask on the Color Fill 1 layer until I filled it with black, made a selection and filled it with white and then resized that beyond the canvas bounds. I'm not sure why you'd want to do that but maybe you can tell me so I can understand your workflow?
In the meantime, this workaround should work for you: Select all the layers in your doc or just the ones being affected by the mask on the Color Fill 1 layer in your example and press Cmd/Ctrl+G to put them into a group. Then click on the Add Vector Mask icon at the bottom of the layers panel to apply that to the group. Export As... will then key off those bounds.