files – tmp directory is not properly configured

A single Drupal instance is failing to write to the tmp directory and I cannot figure out why… All my other instances are fine.

tmp - root:root - 1777

Any tips or tricks I can try?

The specified file 'temporary://fileLT79zp' could not be copied because the destination directory is not properly configured. This may be caused by a problem with file or directory permissions.

DrupalCoreFileExceptionDirectoryNotReadyException: The specified file 'temporary://fileLT79zp' could not be copied because the destination directory is not properly configured. This may be caused by a problem with file or directory permissions. in DrupalCoreFileFileSystem->prepareDestination() (line 488 of /var/www/mysite/core/lib/Drupal/Core/File/FileSystem.php).