Tested versions this is happening on: 4.0.18, 4.4.0-rc5, 4.4.0-rc6 (and some 4.2)
After creating a new replica set (5 nodes) and enabling free monitoring by running
db.enableFreeMonitoring() on the primary, a new URL for the free-monitoring service is created. The URL displays the stats for the primary node only (see attached screenshot). All secondaries show a different URL when connecting to them on the shell.

Expected:

• The URL of the primary should have replicated to the secondaries so that they all point to the same URL.
• The visual free monitoring view should have displayed all 5 nodes (stats) of the entire replica set

Note that:

• After restarting the replica set (with free monitoring enabled) the primary URL is propagated to all secondaries and the view is correct
• Tested on 4.0.0 and works as expected (primary URL is propagated to secondaries)

Attached:

• outputs from the shell for initial URLs of primary and a secondary and after restarting
• Screenshot of visual output after enabling free monitoring (primary)
• Screenshot of visual output after restarting the replica set (expected output)