Issues import failing ojs321

Description of issue or problem I’m having:

We are trying to import into test site data that we exported from our production site. We have in both sites ojs 3.2.1. The import is showing some data related error. We imported all the users, first of all. Then we imported the issue that was exported, but we received the error ERROR: duplicate key value violates unique constraint “publication_galleys_pkey” Key (galley_id)=(34) already exists

In general we do not understand the export/import flow. What are we missing? Should we do it in a different way?

Steps I took leading up to the issue:

We deleted all the issues, future and back issues, and we also deleted all the submissions, before importing. We have the fatal error ERROR: duplicate key value violates unique constraint “publication_galleys_pkey”

What I tried to resolve the issue:

We tried a workaround in order to bypass the problem. We updated the DB row eliminating the duplicate key. The import process goes a bit further, but we had the same problem with another duplicate key Key (galley_id)=(40) already exists.
We also took a look at Native XML Import test fails with no results in OJS 3.2.1-4, that looks partly similar, but could not get any suggestion.
Application Version - e.g., OJS 3.1.2:
OJS 3.2.1

Additional information, such as screenshots and error log messages if applicable: