What to check when Site Template changes are not propagating to sites

Issue

Changes made to a site template (such as adding pages and updating permissions for existing pages) are not propagating to sites, even though the changes are seen in the site template. There are no errors in the logs, and there is no "Reset Changes" button appearing as described in the Propagating Changes from Site Templates documentation.

In the portal-ext.properties file, set the layout.set.prototype.merge.fail.threshold= to a lower value (the default for this property is =3) and restart the application server,
After the server is running again, attempting to propagate the site template changes with the lower threshold active will allow UI warnings to appear as expected (along with the Reset and Propagate button), and errors of the specific failures to be printed in the Liferay log
Though the underlying conflict preventing the template propagation from occurring will still need to be addressed, having the Reset and Propagate button available allows one to reset the merge fail count and attempt to propagate Site changes again. This process provides the opportunity to detect and fix a merge fail when conflicts arise.

The layout.set.prototype.merge.fail.threshold= property was implemented so that in cases where a site template fails to merge, repeated attempts that will inevitably fail are prevented (by setting a fail threshold).
Please note that app data, related resources, and permissions on resources are only copied from a Site template to a Site when that Site is first created based on the template, and are not propagated to the Site after the Site is created through either the Reset or Reset and Propagate features.