Migration is not able to find legacy database tables for some migrations
legacy_database_name.migrate_map_tdmchanneltermparent is a table typically made by the Migrate module to perform a mapping between source DB data and destination DB data. There is typically migrate_map table(s) and for instance migrate_messages table(s).

Be sure to properly Import or Rollback migrations. If you clearing the database by hand and dropping any of these tables, Migrate can get confused. Sometimes I occassionaly MySQL Truncate these tables by hand during my job workflow, but then you need to be careful and understand what migrate is doing -- how it's mapping processed data or registering migrations.

EDIT:

Then as a work around I suggest following the documentation for Map Tables heading section and explicity define the connection you want the mapping table created on. Since you have what looks like a local test migration setup and a Pantheon setup add this ... = new MigrateSQLMap( ... ); in an IF statement to point to the correct Drupal destination connection name.


  When you construct the MigrateSQLMap object, add a fourth argument to
  tell it explicitly the connection on which to create the mapping
  tables.