Ocassionally, it's needed to close a private/fishbowl wiki (see T184961 and T205584 as examples). However, as figured out in T205584, it's not possible to close a private/fishbowl wiki, because only one dblist can take effect in groupOverrides in wmf-config/InitialiseSettings.php.
This can be fixed by moving those dblists to groupOverrides2. By manually testing on mwdebug hosts, this seems to work.