Note that apparently it's just impossible to place any wikilink (or external link by URL), whatever the target or the display text it contains, we always get a warning and a "fuzzy" status for the saved message.

Apparently it seems that those two messages are part of two different groups:

• Global Blocking - User interface (ext-globalblocking-user)
• Wikimedia Messages (ext-wikimediamessages): the most recently added message group (that has another issue, see https://phabricator.wikimedia.org/T332519)

Those groups reuse the same message ID, but only the 2nd of these groups was recently changed in sources to include the wikilink; so there are conflicting IDs within the same target namespace (MediaWiki:).

May be the message for the 1st group should contain the same wikilink as well and the two messages should have not been part of the 2nd message group.

Also I think that the wikilink targets inserted as part of the message may not facilitate the reuse of this "Global Blocking" feature outside Wikimedia, because they would go to Wikimedia MetaWiki. This could conflict with Miraheze and BlueSpice wikis that have their own "Meta" support pages. The target should then probably be passed as a "$1" tvar, so that it can be tuned separately, depending on the wiki farm used (if there's one, may be it is no the same wiki and its local "M:" interwiki could be used for something else, such as a main support site, or a generic policy page describing multiple policies in the local "Project:" or "Help:" namespaces, not specific to a policy but possibly using target anchors).