Just to follow up on what we did after @felix and @nabinhait shared their suggestions, here is the summary
- we increased the session timeout on nginx up to 30 min
- we increased the session timeout on gunicorn up to 30 min
- we trippled the number of workers to start by gunicorn vs. its default value
The combination of those three configuration changes helped to cook our noodles, and we were able to load the batch import file with the size of about 5k records (for Address DocType) to an instance of ERP Next with Production mode set on.
Thank you once again for helpful advise.