as described in your article: https://docs.sophos.com/nsg/sophos-firewall/17.5/Help/en-us/webhelp/onlinehelp/nsg/sfos/tasks/MicrosoftRemoteDesktopGateway2008andR2.html
As soon as a new HTTP based rule configuration has been created and saved or an existing HTTP based rule configuration has been altered and saved, all HTTP based business rules will be restarted. Any underlying client connection using a HTTP based business rule will get lost and has to be re-established.

This should not happen, and it should be corrected.