On a relatively clean install of 1.26, I'm getting this error with only Extension:Comments enabled:
Notice: Did not find alias for special page 'CommentIgnoreList'. Perhaps no aliases are defined for it? [Called from SpecialPageFactory::getLocalNameFor in /var/lib/mediawiki/includes/specialpage/SpecialPageFactory.php at line 645] in /var/lib/mediawiki/includes/debug/MWDebug.php on line 300
Error occurs on pages with comments and Special:SpecialPages
Tried both require_once and wfLoadExtension(). Related: https://www.mediawiki.org/wiki/Manual:Notices_and_error_messages