When someone places an order, goes to Paypal website, login to Paypal account, and pay with no issues at all, but when coming back to website it gives an error 500. The order is not created, but all the order info are in the quote tables. It don't show any error in the logs at all, just after a little while start showing the error 'The "xxxxx" order ID is incorrect...'.
"What was tried?"
So I thought about creating a clone to disable every module to see if was an error in any module, but funny thing, it all works fine in an exact copy of the live website. The only differences that I can remember are Cloudflare (the clone don't have it) and the traffic in the website (same thing, in the clone it's just me), I tried to test in the live website with only like 2 customer and error still persist so I'm not sure that traffic is the problem.
Now I ask, what can cause this? What can I do to debug this?
So I tried to disable Cloudflare (Pause in website), and all ended the same, so I think I can say it's not cloudflare fault.