If shared repo database contain a table prefix, $wgGlobalUsageDatabase should be dbname-prefix. I found getDBname() isn't contain the table prefix, so Globalusage not show on File page. I found getDomainId()result is dbname-prefix, but I don't know if it 's right use, and if my setting wrong in Globalusage.
The code in GlobalUsageImagePageHooks.php line118(Github):
$dbr->getDBname()!=$wgGlobalUsageDatabase