[Support] Update troubleshooting-cloudflare-5xx-errors.mdx

Author: ngayerie

src/content/docs/support/troubleshooting/cloudflare-errors/troubleshooting-cloudflare-5xx-errors.mdx

@@ -118,12 +118,13 @@ HTTP error 503 occurs when your origin web server is overloaded.
 
 ### Common causes
 
-There are two possible causes identifiable by the error message:
+There are different causes identifiable by the error message or the location of the error:
 
 - Error does not contain `cloudflare` or `cloudflare-nginx` in the HTML response body. In this case, the issue is likely from your origin server.
 - Error contains `cloudflare` or `cloudflare-nginx` in the HTML response body. In this case, the issue may stem from Cloudflare.
+- Error is only visible in the logs or analytics
 
-Additionally, `503` status codes in logs or analytics may result from [unsuccessful prefetches from Speed Brain](/speed/optimization/content/speed-brain/#how-speed-brain-works).
+Additionally, `503` status codes in logs or analytics may result from .
 
 ### Resolution
 
@@ -141,6 +142,13 @@ If the error contains `cloudflare` or `cloudflare-nginx` in the HTML response bo
 - The time and timezone of the `503` error occurrence
 - The output of `www.example.com/cdn-cgi/trace` from the browser where the `503` error was observed (replace `www.example.com` with your actual domain and hostname)
 
+#### 503 Error only visible in logs and analytics
+
+These errors result from [unsuccessful prefetches from Speed Brain](/speed/optimization/content/speed-brain/#how-speed-brain-works) and can be discarded. 
+These errors are not visible to visitors of your website.
+[Speed Brain](/speed/optimization/content/speed-brain/#enable-and-disable-speed-brain) can be disabled for the zone if needed (this feature cannot be disabled for a specific path).
+
+
 ## Error 520: web server returns an unknown error
 
 This error occurs when the origin server returns an empty, unknown, or unexpected response to Cloudflare.