Duplicate key value violates unique constraint "pg_type_typname_nsp_index" error

Using PostgreSQL 15.16, I have some SQL for creating a materialized view that's inside a larger transaction which
randomlyemits the following error: 

ERROR:  duplicate key value violates unique constraint "pg_type_typname_nsp_index"
DETAIL:  Key (typname, typnamespace)=(largetable, 20488) already exists.

The error doesn't happen 100% of the times I try to execute this transaction. Maybe 30% of the time? Also, I've had it
happenon multiple separate PostgreSQL servers. 

I'm not entirely sure how to interpret these ERROR and DETAIL messages. Can someone explain it?

I've tried the following queries to try to figure out what typnamespace = 20488 refers to:

SELECT nspname FROM pg_namespace WHERE oid = 20488;
SELECT count(*) FROM pg_catalog.pg_type WHERE typname = 'targetable' AND typnamespace = 20488;

Neither query provides any useful information. The latter always returns zero immediately immediately prior to the SQL
error.

Here's the (slightly sanitized) SQL which causes the error:

CREATE MATERIALIZED VIEW someschema.largetable AS
(
   SELECT
      row_number() OVER () AS __row,
      sub.*,
      public.somefunc1(afield) AS s_result1,
      public.somefunc2(anotherfield) AS s_result2,
      public.somefunc3(somefield1, somefield2) AS s_result3
   FROM (
      SELECT * FROM someschema.largetable_upd_1
      UNION ALL SELECT * FROM someschema.largetable_upd_2
      UNION ALL SELECT * FROM someschema.largetable_upd_3
      UNION ALL SELECT * FROM someschema.largetable_upd_4
      UNION ALL SELECT * FROM someschema.largetable_upd_5
      UNION ALL SELECT * FROM someschema.largetable_upd_6
      UNION ALL SELECT * FROM someschema.largetable_upd_8
      UNION ALL SELECT * FROM someschema.largetable_upd_9
      UNION ALL SELECT * FROM someschema.largetable_upd_10
   ) sub
);

public.somefunc1, public.somefunc2, and public.somefunc3 return three types defined in PgSphere. I have the latest
PgSphereinstalled. 
Any ideas as to how to eliminate the error?

My first thought was to change the asterisks to explicit lists of columns.

Any assistance would be appreciated!

Thanks,
Ed