New browser tab needs to wait for old tab to finish loading to start loading

Scenario:
This happened after Upgraded Cloudflare to Pro, not sure whether it is the cause and how to fix it.

  1. A wordpress site wp-admin backend connected through cloudflare proxy, set to cache “by pass” rule
  2. Chrome Tab #1: Open a post edit page and save it. This save process will take about 20s to complete.
  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 listing all posts
  4. Chrome Tab #2 must wait for tab #1 to finish its task then only it will load. The “network tab” status says “pending”
  5. Firefox Tab #1: While Chrome tab #1 save post is still running, open any page from the same wp backend example: /wp-admin/edit.php on Firefox, the page will load properly with no issue (dont have to wait for chrome tab #1 to finish to load).
  6. The case is same vice versa with chrome and firefox browser.
  7. The scenario does not happen on another similar site with similar setup but with cloudflare free.
  8. The scenario did not happen before upgrade to Cloudflare pro.
  9. The scenario always happen when tab 1 runs any long running script. Tab 2 will always need to wait for tab 1 to finish executing its script before loading any other page from the same wp-admin. Tab 2 will end up as Error 524 Cloudflare cannot reach server because its busy if tab 1 script runs too long.

Question:
What is going on here and how to solve it?

I don’t see why there would be a difference between Free and Pro, but you’ve been thorough in your investigation.

The next thing I would try would be to “Pause Cloudflare on Site” from the Overview page. This will bypass Cloudflare, but wait 5 minutes for it to take effect. Then try your test again.

It’s behaving like there’s some sort of Rate Limiting because all of these connections are most likely coming through the same back end Cloudflare Proxy IP address.

@ sdayman
By pausing cloudflare for testing would it also stop cloudflare from handling nameservers dns redirection?
If so, then for this test it will require to change the nameservers of domain so that it would not go to cloudflare.
If this is the case, this would be dangerous to do testing this way, as propagations may result website downtime of up to 72 hours and also to switch back after testing

Pausing puts the domain in DNS-only mode. So page rules will not apply. You will effectively have your site just the same as it was before it was added to Cloudflare.

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