This post:
https://www.bikeforums.net/20527022-post376.html mentions Darth Lefty. This post:
https://www.bikeforums.net/20530300-post377.html mentions Gugie. When I went to edit the post (thinking I'd muffed something), I saw the correct BBCode for the mention (mentally remove the spaces before/after the brackets):
[ MENTION=339610 ]Darth Lefty[ /MENTION ]
It's just not being displayed. This has been an issue with the mobile skin for quite awhile. I just started noticing it with the main skin/theme. Likely related to the latest update of the forum software.