There are a few entries with sequences that are breaking Zotero's import — specifically, {\} appears in a few titles without a \ before the first {. I'm not sure why those are there or what the correct behavior would be, but Zotero's translator will skip the rest of the file once it gets to the { character.

Issue created, but for now you can fix those entries manually and the import should go through (though I didn't test the whole file with those fixed, so there could be other problems). It's also possible that the Better BibTeX plugin can handle this.

You don't need to go through 2144 entries — I told you exactly what the problem is, which appears in three entries. It would take 30 seconds to fix it on a computer. There are text editors for iOS, though obviously that's a little more complicated. But there's no reason you should be waiting for us to import here. Any change we made here would just be to make Zotero a bit more forgiving of invalid BibTeX, but this is a bug in Paperpile's BibTeX output.

I guess I'm just lazy :)

I've been waiting for Paperpile to add ability to edit notes on my IPad for the last 1.5 years, they didn't, so now I'm going through all other reference managers to see if there's a better one to transition to

Again, there are three affected entries.

OK, replacing all "{\} " with "" I now get 2052 entries out of 2144

Is there some automatic way to find all unbalanced braces?

These are all seem to be articles from citeulike->paperpile bibtex transition, so paperpile .bibtex import is able to handle this kind of syntax without aborting the rest of the import

These are all seem to be articles from citeulike->paperpile bibtex transition, so paperpile .bibtex import is able to handle this kind of syntax without aborting the rest of the import

No, that doesn't follow. Judging by their online converters, Paperpile does appear to handle this invalid BibTeX (which makes sense, given that they also produce it), but CiteULike could have included all sorts of gibberish in fields and it could still have been encoded as valid BibTeX. This is just data in your Paperpile library, which has nothing to do with BibTeX — you could have typed it in manually. The only thing relevant here is that Paperpile is generating invalid BibTeX when you export your library.

It's also not a given what the correct import behavior is. It probably makes sense to try to detect an unclosed brace, in the name of Postel's law, but we need to investigate whether the correct behavior is specified anywhere and/or what the main BibTeX programs do. That's why this isn't necessarily an immediate fix and why I said you shouldn't wait for us to do the import.