Link scrubbing to same domain as community?

Will you add that domain the whitelist in Administration -> Moderation -> Content Filtering -> Allowed Hosts. There are several checks on urls, one of which is to see if its resolving internally (potential SSRF attempt) and if so, it will strip it out.

I did add the domain to the whitelist (which caused the site to restart on save FYI) but that did not resolve the issue.

The link is stripped on save, not render so any content that was subject to this will have the text only still. Did you retest with new content after the save?

Yes, I expected the previous content to have been stripped, so I retested after the save with new replies and a new thread. Same results.

did you include www (per your example)? if so you'll need two entries, one with and one without. Note: The preview within the editor (Tools -> Preview) can be used to test without actual posting.

I did not (as the example on page had stripped the preceding data) but after including www, it does now work.

Are wildcards allowed in this field so all subdomains could be included without explicit entries (e.g.: *.mycompany.com)?

Wildcards are not supported for this field.

That is unfortunate.