Found another way to recover a lost quick note: Today, on the quick-notes toolbar widget, as soon as I hit "Save to Evernote," everything I wrote disappeared and couldn't be found in the app or on the web. (TBH I didn't even want to use the dumb toolbar feature; I hit command control N b/c I wanted to do a regular note in Preview but thought, Huh, I like Evernote, maybe this'll be fun 🙃 ) Thanks to this thread I searched for quick-note-preserved.obj. Like it was mentioned earlier, renaming to .txt doesn't work.
But what DOES WORK is right-click and selecting to open it with Notes. You'll have to wade through a bit of code at the beginning and the end, but your lost note will be waiting for you in the middle of it. It weirdly won't let you properly copy and paste it (::laugh, sob::) so you'll have to AirDrop that note to your phone if you have an iPhone.
What a trash glitch though. Can they fix this already??