Found the issue - I just had to look for the 1610th entry in the .1pif file, delete those two lines and see if the import went further. It did... 2,603 items were imported, so that adds exactly up to the 2,532 +72 (archive) - 1 (the culprit entry).
So that enpass can fix the bug, the issue was caused by a large 1Password note that contained my PGP keys - looks like that note was probably too large. It had 182,067 characters over 2,718 lines of text, and looks like this (see screenshot).