id_internalwikimedia is a recently created private wiki (T196747). Uploads seem to be working fine to the wiki, but thumbs (via thumb.php) don't seem to be working.
Thumbs are giving 404s and FileOperation.log says the thumbs don't exist. The swift containers for the thumbs are empty, but the originals are there
2018-08-03 15:47:21 [W2R5CQpAADwAAHzvn4YAAAAL] mw1265 id_internalwikimedia 1.32.0-wmf.15 FileOperation DEBUG: FileBackendStore::preloadFileStat: File mwstore://local-swift-eqiad/local-thumb/c/cd/WMID_RK_USD_September_2013.jpg/431px-WMID_RK_USD_September_2013.jpg does not exist.
reedy@deploy1001:~$ mwscript eval.php id_internalwikimedia
> $b = FileBackendGroup::singleton()->get( 'local-multiwrite' );
> $path = $b->getRootStoragePath() . '/local-thumb';
> foreach ( $b->getFileList( [ 'dir' => $path ] ) as $file ) { var_dump( $file ); }
> $path = $b->getRootStoragePath() . '/local-public';
> foreach ( $b->getFileList( [ 'dir' => $path ] ) as $file ) { var_dump( $file ); }
string(32) "0/00/REDACTED"
string(47) "0/00/REDACTED"
string(39) "0/00/REDACTED"
(etc)
>