Time out opening second page in same browser with long running page load

Scenario:
1. A wordpress site backend.
2. Chrome Tab #1: Open a wordpress backend example: /wp-admin/run-long-php-script/ which runs a long php script which will continue to load for a long time.
3. Chrome Tab #2: While tab #1 is running open another tab #2 on same Google browser and access any page from the same wp backend example: /wp-admin/edit.php
4. Chrome Tab #2 cannot load and will time out. It can only load properly when Chrome tab #1 php execution finish its task.
5. Firefox Tab #1: While Chrome tab #1 php long script is still running, use Firefox browser to open any page from the same wp backend example: /wp-admin/edit.php, the page will load properly with no issue (no time out).
6. The case is same vice versa with chrome and firefox browser.
7. Domain is running trough cloudflare with no cache on /wp-admin/*
8. Site is using php fpm 7.3

Question:
What is going on here and how to solve it? Or if unclear, how to find the origin of the issue?