"Find Includes" works only for multiexcerpt-include, does not work for multiexcerpt-include-macro
MultiExcerpt-Server has two possible names for the MultiExcerpt-Include macro:
This is done to support migration scenarios (Server --> Cloud or Cloud --> Server).
The normal macro name, for a deployment that has not been migrated from Cloud to Server and has not ever been processes for migrating from Server to Cloud, is multiexcerpt-include.
I rare circumstances, if a migration has occurred, the "Find Includes" button will not work. It does not find includes that use the multiexcerpt-include-macro name.
In addition to the migration scenario there is the possibility of an admin configuring the enable/disable status of the multiexcerpt-include-macro without knowing what that does. It is possible that someone could enable that, even for a short time, and when it is enabled any include will be created with the name multiexcerpt-include-macro.
To diagnose this problem look at the Storage Format of the page with the include on it to see what the macro name is. It could also help to look at the MultiExcerpt macro in the Confluence app management tool to see if the multiexcerpt-include-macro module is enabled, though if it is not enabled it will not tell the whole story: it could have been enabled at some time in the past.