Schema change, add columns to the table, never end. Table locked

Running alter table add column statement on same table.
The Jobs for all statements in running state but never ends.
From this point we can’t perform any schema changes on the table.
This happening second time in production, but never happening in testing environment.

Please help.

Two questions:

  1. What right way to perform schema changes.
  2. How fix/resolve locked schema

Thanks