Unable to connect to a RDP Gateway Session Host when it is behind IIS running Application Request Routing.
IIS -> Remote Desktop Gateway Web Access -> Remote Desktop Gateway Session Host.
Everything worked internally, connecting externally to the web server works fine and the actual rdp file that is downloaded and runs looks fine (correct server address, correct gateway address) but still just times out upon trying to connect.
Turns out to be the IIS ARR at fault.
Click on Server Farms -> gatewayurl.domain.com -> Proxy -> Buffer Settings -> Set Response buffer threshhold (KB) to zero (0) -> Apply
Refresh your RDWeb page and it will instantly connect!
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