I was simply looking through a specific notebook when they spontaneously started being deleted. I was only using my scroll wheel and it doesn’t seem to have been synchronizing. I have no idea what happened and after they were deleted, I cancelled the synchronization that began.
I still have everything on my phone but there doesn’t seem to be an export option. Is there anything I can do?
You could change the sync target to a different provider. For example, if you use OneDrive now, switch to Dropbox, then sync. You can then sync with that target from the desktop client to recover all your notes. Make sure you export them all to JEX at that point to have a backup.
When I change the sync target on my desktop, won’t it delete the notes on the new sync target from my phone?
No. Syncing should bring the new stuff from both sources and merge them.
This didn’t work and did exactly what I feared. The deleted items still haven’t returned after I changed the sync target on my phone that still had the lost notes, then synced to that target from my desktop. On top of that, when I synced on my desktop it said it deleted remote items making me think it just deleted what I had on the new sync target. 
I turned off my phone’s wifi before doing this so technically everything is still on my phone. Please help me not lose these very important notes! How can I fix this?
Very hard to help here because it depends on what’s on your phone, what’s on the sync target, on desktop and what’s the sync state of the apps.
Did you make a backup of your desktop app, as was suggested?
For the phone notes, are there many of them? Otherwise I’d just manually copy and paste the Markdown and be done with it.
There are probably easier ways to do this, like what I’ve suggested at the beginning but again it depends on how are your apps setup and their sync state.
My phone is a Moto Z2 Play running Android 8.0. I was syncing to dropbox from both my desktop (on Windows 10) and my phone, obviously. Then my notes suddenly got deleted so I did what you suggested and changed the sync target to OneDrive on my phone (which still had all my stuff). When I did what you said, all that happened is the notes were also deleted on the new sync target…
I didn’t make a recent enough backup.
Correct me if I’m wrong, but shouldn’t “new sync target” be a new sync target? Not an old one? If you setup an entirely new sync target, it can’t delete the notes from that new sync target, right?
I guess I’m just missing something.
It was a new sync target. I had never used OneDrive before. But when I then also synced my desktop to this new sync target, it erased what was there. I just lost hundreds of extremely important notes.
I even disabled sync on my phone. I just opened my phone to find out it synced anyways and now I’ve even lost the notes on my phone.
Looks like I’m going back to evernote…