If you look at EXPLAIN.DDL, there is no schema on any of the objects. So the schema defaults to the user who creates them. To see the explain in Command Editor, you have to be connected as the user that created the explain tables.
No Explain instances (plans) were found for database MERLIN, source pattern: %.% for explain table schema "DB2INST1
Maybe it tell you sum more information about the problem .
The explain tables are exists in the db:
$ db2 list tables for all |grep EXPLAIN
EXPLAIN_ARGUMENT DB2INST1 T 2010-12-15-17.05.00.553209
EXPLAIN_DIAGNOSTIC DB2INST1 T 2010-12-15-17.05.20.301618
EXPLAIN_DIAGNOSTIC_DATA DB2INST1 T 2010-12-15-17.05.25.426265
EXPLAIN_INSTANCE DB2INST1 T 2010-12-15-17.03.05.584184
EXPLAIN_OBJECT DB2INST1 T 2010-12-15-17.05.06.728447
EXPLAIN_OPERATOR DB2INST1 T 2010-12-15-17.05.11.129463
EXPLAIN_PREDICATE DB2INST1 T 2010-12-15-17.05.14.243679
EXPLAIN_STATEMENT DB2INST1 T 2010-12-15-17.04.47.788480
EXPLAIN_STREAM DB2INST1 T 2010-12-15-17.05.17.096144
EXPLAIN_ARGUMENT MAXIMO T 2010-12-15-17.17.00.334363
EXPLAIN_DIAGNOSTIC MAXIMO T 2010-12-15-17.17.08.931425
EXPLAIN_DIAGNOSTIC_DATA MAXIMO T 2010-12-15-220.127.116.11079
EXPLAIN_INSTANCE MAXIMO T 2010-12-15-18.104.22.1689700
EXPLAIN_OBJECT MAXIMO T 2010-12-15-17.17.02.371373
EXPLAIN_OPERATOR MAXIMO T 2010-12-15-17.17.03.270327
EXPLAIN_PREDICATE MAXIMO T 2010-12-15-17.17.04.403945
EXPLAIN_STATEMENT MAXIMO T 2010-12-15-22.214.171.1245207
EXPLAIN_STREAM MAXIMO T 2010-12-15-17.17.06.778140
Did you migrate your database from previous version of DB2? I had similar problems after upgrading to new version. You have to run db2exmig command to migrate explain tables. The command needs to be executed individually for all schemas with explain tables.