Cloudflare human verification corrupts uploading files

Hello, I have been usung Cloudflare free version for two years and then last fall in 2023 I upgraded to the pro version.
We have an old forum and some of our members can upload images. The process is similar to this forum BUT we are using an attach manager that first open a window/box where one select images and submit.

A week ago this function stop to work. Now suddenly it shows a

  • Cloudflare verification window and within a second it changes to
  • Verification success window and then it goes back to our
  • Forum start page.

I have enclosed images here so you can see the process how it doesn’t work.
I need to sort this out do you have any ideas what could cause it?

thanks in advance

After reading Cloudflare security event logs I changed The Cloudflare OWASP Core Ruleset to default settings and it started to function properly again.
So no issues at the moment.
Thanks for listening…