Issue
Newly setup Remote Desktop Web Access service with RD Web Access, RD Gateway and RD Session Host roles located on the same server. Everything was working during testing a day before, but next morning external users couldn't connect to remote computers via the Remote Desktop Web Access website. Internally everything was working fine.
Resolution
Issue was resolved by manually specifying RD Gateway server in RemoteApp Manager settings (originally it set to detect RD Gatewayautomatically):
- Open RemoteApp Manager mmc
- Action > RD Gateway Settings
- Select "Use these RD Gateway server settings" and enter externally resolvable RD Gateway FQDN.