Re: pg_upgrade and publication/subscription problem

AFAIU the main problem in your case is that you didn't block the write
traffic on the publisher side. Let me try to understand the situation.
After the upgrade is finished, there are some new tables with data on
the publisher, and did old tables have any additional data?

Are the contents in pg_replication_origin intact after the upgrade?

So, in short, I think what we need to solve is to get the data from
new tables and newly performed writes on old tables. I could think of
the following two approaches:

Approach-1:
1. Drop subscription and Truncate all tables corresponding to subscription.

2. Create a new subscription for the publication.