When you create a post (blog, forum, wiki) and add some project number or JIRA ticket number in the beginning, linked to your Helpdesk, or other system, this link gets removed in the mail notification and activity stream.
When your JIRA number now contains a string like .TLD-### the process creates a new not working link.
<p dir="ltr">Check <a href="https://jira.stoeps.de/important.de-12345">important1.de-12345</a></p>
Now we save this and have a look into the Activitystream (same happens with mails like newsletters):
<a href="http://important1.de-12345" target="_blank" rel="nofollow noopener noreferrer">important1.de-12345</a>
So our working link to the project, or ticket got removed and new one which is not valid is created.
This works with strings with a dot following a valid IANA TLD like de, us, hr, xxx, com following -=+ and string, number.
The opened ticket is closed with works as designed, so please overthink this design, as it disturbs users and produces 404 links.
Removing a working link already needs an explanation in my eyes, but adding not working links which produce helpdesk tickets, as the users won't understand this behavior is not understandable at all.
Example wiki page: https://preview.hclconnections.net/wikis/home?lang=en-us#!/wiki/W2dee466b5cd1_40bc_8937_6e3204295014/page/Test%20for%20idea
Check recent updates for the link: https://preview.hclconnections.net/communities/service/html/community/updates?communityUuid=58d4fc9d-a82c-442f-904c-ad138df5fafd&filter=all
Sadly, I can't share a screenshot of the behavior, but it is easy reproducible in any Connections environment. https://support.hcltechsw.com/csm?id=kb_article&sysparm_article=KB0092986 explains something similar, this user created his project numbers with xxx and got some adult links in the newsletter instead.
So with the KB info I could just all known TLD to the exclude list, but I don't think this is intended.
Most of the mail clients I use do link recognition on their own (like HCL Notes or Outlook), so I see absolutely no use case why this should be designed like this.