Hi @robkam, thanks for taking the time to report this!
https://www.mediawiki.org/wiki/Extension:ExternalLinks#MediaWiki_.3E_1.21 implies that the extension is located on GitHub, so https://github.com/roman-1983/mediawiki-ExternalLinks might be the place for bug reports instead.
However the page also lists @Subfader as an author hence CC'ing here.
In general, this report unfortunately lacks some information - adding a more complete description is welcome with version information, clear steps to reproduce, what is expected, and what is the actual result. Problems that others can reliably reproduce can get fixed faster. Thanks! :)
Thanks, I hope this is better:
Installing the extension on MW 1.27.1 as per Example configuration. Extension is listed at Special:Version but Special:ExternalLinks goes to an empty non-wiki page. On wiki pages the sidebar link Validate external URLs is missing. If option $wgELuserRight is used the whole wiki doesn't load.
Yes it's on GitHub, I'll report the bug there as well.