We've fixed the FlowMention template as per T106575: Template:FlowMention missing, new mentions of users are broken
The broken mentions that were created when the template was broken are still there, and need to be fixed.
Examples:
https://ca.wikipedia.org/wiki/Tema:Slvykcwboruvrk4n
https://pt.wikipedia.org/w/index.php?title=T%C3%B3pico:Slkw2n4nvfpo3luu&topic_postId=slkw2n9n5lp8127a&topic_revId=slkw2n9n5lp8127a&action=single-view
Filing this as Unbreak Now because these wikis are big Flow supporters, and we shouldnt' leave their stuff broken.