When using Quick Export As PNG, if I quit photoshop before the icon has actually shown up on my desktop, then it's just lost forever. It should have a "this file is being saved in the background" warning message the same way the "save" command does, not just silently cancel the write if you happen to quit before it has silently finished writing.
Create a large document (i.e. 24000x6000)
Fill it with noise or something to make the resulting file take longer to write
Open an Explorer window to the folder you're intending to save it to (or make sure you can see the desktop if you're saving there)
Do 'Export > Quick Export As PNG'
Before the document's icon appears in the folder that you're saving to (this takes about 1m30s on my machine), quit Photoshop.
Photoshop immediately quits as though it weren't in the middle of something important, and the PNG it was supposed to export never appears.
I know that the simple workaround is "well just don't quit photoshop while you're waiting for a file to appear", but again, the files that I'm dealing with take well over a minute to finish being written, and I have to just sit there and stare at the desktop before I can go back to photoshop and close everything down -- and more importantly, the fact that the file isn't written isn't obvious to people who haven't already memorized the existence of this bug, which means that they can easily lose data by just asking Photoshop to begin shutting down and expecting that it would finish its tasks first. (I was scanning in a document, and straightening it, and tweaking the levels, and then saving the result as a PNG, so I don't have any other document to fall back on; I have to start the entire scan & cleanup process over again.)
Thank you, Andrew, for reporting this issue. I was able to reproduce it and have logged it in our tracking system. Beyond using Save As (which is not particularly quick), I would suggest using an Action. If you add the one step of saving as PNG, the action will be a pretty quick export. If you need to change the output file name at the time of saving, check the box next to the action. It has a tooltip: "Toggle dialog on/off". When you run the action, the file browser will appear. PNG sho...