In the moodlelib.php (https://github.com/moodle/moodle/blob/43c7557e847f8520eb55a7e78ba94180d27aaa42/lib/moodlelib.php#L10041) is a NFS incompatible remove_dir function. This function triggers this https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=57696 error and could be resolved by https://forums.freebsd.org/threads/problem-wiith-removing-folders-on-nfs.82034/ .

This fix proposed in the thread does have some sort of extended race condition, however the compatibility would be increased a lot. It is mostly triggered when installing the PHPUnit suite.