Why is pdf not displayed and get erorr 520 when use cloudflare?

I have an asp.net webform project, and it works correctly when I use in smarterasp server with SSL
But when i use cloudflare , every pdf view cannot be displayed inside the site and get error 520.
What is the reason and how can the problem be solved please?

Did you click on the 520 link in your post?

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