It appears to be a long time since HexEditor has been updated (according to the project's downloads listing on SourceForge)…
Currently, I updated to Notepad++ v188.8.131.52 (Unicode) and after update it displayed that HexEditor was moved to the disabled folder due to incompatibility (I didn't type up the full dialog box text when I saw it).
I hope HexEditor wasn't abandoned… it really IS a great plugin for such a great Windows Notepad replacement!
Running Windows XP Professional (but I doubt that will mean anything).
I hope too that HexEditor continue to be maintained but I have some doubts.
User interface and features make it a really great tool and I would just love to use it. There is one HUGE problem: it does not display binary files correctly (as a hex editor should - that is what is it used for). See "NPP v5.4.5 and HEX-Editor (both versions) - ID: 2823651":
As this problem seems to be related to NP++ itself rather than to the plugin and renders HexEditor pretty much useless, Jens might have thus abandoned the project.