Parent List is not showing properly for the query

We have query with union of two tables from different sources and on top of union added select projection which is failed to read all parents form thee query. Below is the sample query and exception in the logs:

SELECT * FROM
(select 1, 2 as join_column FROM A
UNION
SELECT 1, 2 as join_column FROM B)
Left outer join
C as or1
ON or1.entity_id=join_column

Error: 2021-01-11 15:38:02,798 [qtp1905079199-313] WARN c.d.s.jobs.metadata.AncestorsVisitor - Failure while extracting parents from sql. Unexpected 1st operand in AS: UNION. SQL:
UNION: UNION {
0: UNION: UNION {.
.
.
.
.

Could please help us with this issue?

@PranayKamuni

Are you able to share the Dremio job profile?