Random Error code 408 when using cloudflare with grpc

Some of our users are getting error code 408 when trying to connect to our server when we proxy our traffic using Cloudflare.
Once we select the DNS only option ] the error disappears From all the users.

The Cloudflare Ip that is mostly affected by this error is:197.234.242.42

So a HTTP 408 is not a response code that Cloudflare will generate - so this means your origin is returning that code to Cloudflare.

The way to debug this would be to check your origin server access & error logs to understand why it is returning 408 on these occasions. One possible cause is rate limiting at your origin of the Cloudflare IPs - so it’s worth asking your host to check and ensure all of the Cloudflare IPs are allow-listed from any rate limiting you do. If you want more details on this - the fixes for a 522 error has much of the same advice you should follow: Community Tip - Fixing Error 522: Connection timed out

Actually Cloudfalre returns error 520 to the client.

Error code 408 is what is what our nginx server logs are showing as the error that happened.

The weird thing is we have been running the server without Cloudflare for the past 4 hours and the error has not happened since then.

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