Yeah, I updated to v10 without realizing it was a major update. Spent less than 1 minute looking around and pulled the ripcord and parachuted out of there; went back to v6, and started to check out other note apps, which is how I found Joplin. The release of v10 was horribly mismanaged, and I'm sure it destroyed a lot of goodwill amongst Evernote users.
Since you lost a lot of note titles in the trouble enex, might be worth hanging onto those notes in EN and keeping them isolated in Joplin. If @laurent can figure out the problem from the enex you posted, and update Joplin to resolve it, you can update the app and reimport.
Ok it seems the ENEX file is actually invalid, and indeed even Evernote cannot import it back (it imports only 18 out of the 50 note).
Unfortunately in this case the file is so broken that there's no generic fix that can be added to the app for it. You can fix the file yourself though by opening it in any text editor and replacing all the strings <![CDATA[>]]> with >. After that it should import all the 50 notes without any error.
Yes I don't know how they can get everything so wrong. It's 2021 and with their billions and army of overpaid engineers they haven't yet figured out how to escape HTML. Unless they are breaking their export file on purpose to prevent users from migrating, who knows, but in any case it's either maliciousness or extreme incompetence.
I don't think it was maliciousness in terms of trying to lock users in - after all, ENEX backups are lossy even for Evernote users. And probably not extreme incompetence - I think their revolving door of CEOs and constantly changing priorities meant a number of things were half baked and never properly implemented. Perhaps that will change now that they have unified their core codebase.
But for sure, a lot of their "power users" had workflows broken without any meaningful warning, so plenty of them are not going to stick around to see if the elephant is going to finally regain its footing. For users who use a note app all day, every day (as opposed to those who clip items a few times per week), trust is critical. Evernote, which billed itself as a "second brain" didn't fully appreciate the importance of the trust their users placed in EN. And once broken, regaining that trust is no easy feat.
I've been on the Evernote forum for years, and I've seen users complain about every change, but I've never seen so many significant complaints as I have with v10. And I've never seen so many people not just threaten to leave, but actually leave, with many others evaluating other note apps as part of a potential exit strategy.
I was already looking into alternatives, to be honest. But v.10 pushed me to take the plunge. (They actually removed the one feature that had me hanging on -- the ability to use a single shortkey combo to paste straight into a new note.) But, yeah...it seems as if they took the Microsoft approach. lol You know, "let's release it broken and fix all the problems later."
I'm willing to deal with the extra work of just manually fixing broken notes, if need be.
The primary reason I switched, though -- and the primary reason I chose Joplin -- was security. Call me paranoid, but I don't necessarily trust Big Tech to not start using sync as an opportunity to make notes disappear if they contain keywords that red-flag them as "socially-unacceptable" content. As a Christian, a political conservative, and an alternative medicine advocate, I'm not exactly their favorite person.