Docs: Troubleshooting Proxies (#12119)

* Docs: Troubleshooting Proxies [ci skip]

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* Maz suggestion [ci skip]

Co-Authored-By: Maz Ameli <maz@metabase.com>

* fix a typo in a suggestion I made :b

Co-authored-by: Maz Ameli <maz@metabase.com>

docs/troubleshooting-guide/index.md

@@ -12,4 +12,6 @@
 
 ### [Incorrect results due to time zones](timezones.md)
 
+### [Problems with saving questions/dashboards or blank page](proxies.md)
+
 ### [I think I found a bug](bugs.md)

docs/troubleshooting-guide/proxies.md

+If you're experiencing problems where attempting to save a question or dashboard sometimes fails, or Metabase only loads a blank page, this might be caused by the use of a proxy.
+
+A proxy could include other functions like a web application firewall (WAF), content optimization, or cache.
+
+Examples of proxies that are known to cause issues with Metabase:
+
+- Cloudflare's Rocket Loader and WAF
+- Azure's WAF
+- PageSpeed module for e.g., Apache
+- Some anti-virus browser extensions or add-ons
+
+## Specific Problems
+
+### Saving questions/dashboards fails
+
+If saving questions/dashboards fails with the save button changing to "Save Failed," or perhaps with the error, "Sorry you do not have permission to see that," this might be caused by either a WAF like Cloudflare or Azure.
+
+- When the save fails, check the Console tab of your browser's Developer Tools for any errors.
+- You should also check the Network tab in the Developer Tools to view the network request. It will usually fail with error code 403, indicating the error is coming from the WAF and not Metabase.
+Clicking on the request will show more information, and looking at the headers will usually indicate where it originated from.
+
+Some WAFs have dynamic protection, which means that the problem might only occur after an upgrade of Metabase, and might go away after a few days.
+
+The solution is to disable the WAF for Metabase. Some services will show which rules were triggered, so it might be enough to disable those rules.
+
+### Seeing a blank page instead of the Metabase interface
+
+If Metabase just loads a blank page instead of the interface, then it is usually caused by content optimization like PageSpeed or Cloudflare's Rocket Loader.
+
+- Check the Console tab of your browser's Developer Tools for any errors involving Content Security Policy (CSP).
+- See if Metabase has been able to deliver the HTML code by right clicking the blank page and selecting "View page source." It might look like gibberish, but it should say `<title>Metabase</title>` near line 25.
+
+The solution is to disable the content optimization for Metabase.