Bug in the plugin forums - double posts - double posting - caused by Cloudflare

Hello Guys
I have a problem with double posts in the simple forums plugin and I know what causes the bug.


In the topic above someone already posted it, but did not receive any solution to it.

The point is when Cloudflare cache is activated, post/topics are posted double.

Here some of my Cloudflare cache settings:
Caching level is set to "Ignore Query String"
Browser Cache Expiration "1 year"
Always Online™ "On"
Development Mode "When ON -> no double posting"

Do you know how to solve this "bug"?

Thank you in advance.