Server got hang while close, drop and recreate child pluggable database

Hi all,

I have used oracle standalone 12c in Linux 64bit.

I have about 50 parent and 100 child pluggable database and these child databases created by using snapshot copy like below:

create pluggable database CHILD_01 from PARENT01 snapshot copy file_name_convert=('/PARENT01/','/CHILD_01/');

alter pluggable database CHILD_01 open;

The users recreate child database with steps: close --> drop child including datafiles --> recreate child. This recreating child database has worked fine. But sometime, some users recreate child databases at the same time (ex:10AM: User01 recreate CHILD_01 and User02 recreate CHILD_02) and the recreating lead to database server got hang (use sqlplus to access to database but unable to access).