https://pt.wikipedia.org/w/index.php?title=T%C3%B3pico:Slkw2n4nvfpo3luu&action=compare-post-revisions&topic_newRevision=slkw6fjhy0e1sd1k

As @Legoktm shows, the addition of a Flow mention at the end of that comment in pt.wiki is legit. The problem is that Template:FlowMention is missing. This problem is related to the implementation of T99891: Remove the colon at the end of mentions in Flow.

The template was missing from a couple of wikis. I've just run the script to add them. The template should now exist for:

• testwiki
• test2wiki
• mediawikiwiki
• metawiki
• enwiki
• frwiki
• hewiki
• officewiki
• ptwiki
• cawiki
• tewiki
• ruwiki
• pawiki
• zhwiki
• wikidatawiki
• viwiki

We plan on enabling Flow by default on (all|a lot of) wikis; I've added a task to make sure we create this template there as well: T107143

Please check the two links in the description. Now the template exists indeed, but the username still doesn't appear in the messages.

(Hm, this might be a problem only in the posts created while the template was missing? If so, I guess it's fine.)

That's because content is stored in HTML & templates are transcluded (or not, in this case) when the content is saved, not every time it's displayed.
It should be fine for new mentions from now on.

The pages fr:Template:FlowMention and zh:Template:FlowMention were not created.

Some others are now linked through
https://www.wikidata.org/wiki/Q20739451#sitelinks-wikipedia

In T106575#1492385, @He7d3r wrote:

The pages fr:Template:FlowMention and zh:Template:FlowMention were not created.

That's because the name is translatable. French has translated it as fr:Template:Mention, and Chinese has zh:Template:Flow提及

Checked on pt.wiki and ca.wiki.

Ran extensions/Flow/maintenance/FlowCreateMentionTemplate.php for cawiki on betalabs.