Mysql: select from information_schema.STATISTICS hanging or slow? never saw a result
20K tables means opening 20K files on the system.  This takes minutes on the typical server.  How long did you wait?

20K tables often means poor schema design.

BTW, the slowness will be solved in 8.0, when the .frm files are moved into InnoDB tables.  Many I_S queries will be a hundred times as fast.