[Major version upgrade] pg_upgrade fails despite passing check mode

postgres@dxxxpgs03:/Dxxxx1/datadg/data13$ /usr/pgsql-13/bin/pg_upgrade -k --check --new-datadir='/Dxxxx1/datadg/data13' --old-datadir='/Dxxxx1/datadg/data' --new-bind$
r='/usr/pgsql-13/bin' --old-bindir='/usr/pgsql-11/bin'
Performing Consistency Checks
-----------------------------
Checking cluster versions                                   ok
Checking database user is the install user                  ok
Checking database connection settings                       ok
Checking for prepared transactions                          ok
Checking for system-defined composite types in user tables  ok
Checking for reg* data types in user tables                 ok
Checking for contrib/isn with bigint-passing mismatch       ok
Checking for tables WITH OIDS                               ok
Checking for invalid "sql_identifier" user columns          ok
Checking for presence of required libraries                 ok
Checking database user is the install user                  ok
Checking for prepared transactions                          ok
Checking for new cluster tablespace directories             ok

*Clusters are compatible*

But then while performing the actual upgrade, it failed saying the "owner of a FDW should be a super user"

So I started the old Postgres 11 again, changed the owner of that FDW to a super user.

Now when I try to run the upgrade (even in check mode) again, it says "new cluster tablespace directory already exists"

Is it safe to delete the new tablespace directories?

What are my options to safely start/upgrade the DB without any chances of data corruption? 

Thanks