Updated Health Checks (markdown)

Health-Checks.md

@@ -37,6 +37,22 @@ If you're on linux, you'll probably have to change the home directory for the us
 
 The update branch setup in Settings/General is for a previous version of Radarr, therefore the instance will not see correct update information in the System/Updates feed and may not receive new updates when released. 
 
+### Could not connect to signalR
+
+signalR drives the dynamic UI updates, so if your browser cannot connect to signalR on your server you won't see any real time updates in the UI.
+
+The most common occurrence of this is on V3 combined with an nginx reverse proxy.  Nginx requires the following addition to the location block for radarr:
+
+```
+proxy_http_version 1.1;
+proxy_set_header Upgrade $http_upgrade;
+proxy_set_header Connection $http_connection;
+```
+
+Make sure you **do not** include `proxy_set_header Connection "Upgrade";` as suggested by the nginx documentation.  **THIS WILL NOT WORK**
+
+See https://github.com/aspnet/AspNetCore/issues/17081
+
 ### Download Clients ###
 
 #### No download client is available ####