Photoshop CC 2018: Exporting @2x stopped functioning correctly

Why wouldn't he simply be using the common Export As dialog? If he is using Generate > Image assets, I hope he comes back and tells us, as that's a very different process.

I believe that the asset generator and the export as both use the underlying generator framework... Just via different entry points, but essentially the same backend.

Maybe someone can correct me if I am wrong?

That sounds very possible—that both Generate > Image Assets and Export As are front ends to the same thing. But the way you interface with each, without even starting to get into the technical page you suggested, is very different. It's common for defaults to get reset when installing a new version, and the simple one with Export As would be the sharpening when upscaling.

If he is using Image Assets and something in the underlying configuration (not something that most users would ever access) has changed, that's a much bigger deal, something he needs to show Adobe, and something Adobe should probably deal with. To my knowledge, Photoshop users are not expected to write their  own configuration, and it shouldn't have changed without making a note of it.

All I know is that I upgraded to PS CC 2018, and continued to use the standard "Export as..." dialog to export assets to multiple sizes—just as I'd always done. Since the update, @2x images look awful on Retina screens (or any hi-res screen), when they used to look sharp and crisp. I contacted Adobe Customer Care via Twitter, and they came up empty, and suggested I come here...

I thought that could be it. Very often when you update, preferences get overridden and return to their defaults. Knowing that Adobe had also enhanced its sharpening routine, that was a place to look first.

When I've encountered something not as expected, I first look to preferences. Have they been changed? If not, have they become corrupted? I could wish there were some way Preferences could be more stable, but they're written to disk on exit, and any number of things along the way can seem to scramble them. Not usually all of them, but just enough we haven't a clue what is going on.  '-}

Unfortunately, when I delete preferences because I think they may have become corrupted, I'm usually too involved in seeing if it solved the problem, and then with reconstructing my preferences,  to remember to take my own advice and save out a clean copy of my personal preferences, dated, in order to restore them more quickly next time.<sigh>