I assume that most of Windows administrators is once in a life tried to configure and use Remote App. That is not a “big deal” for installing and configuring, but some (most) of parameters can be configured only with PowerShell. One of that parameters is changing default RDP port from 3389 to any other port. Changing default RDP port is a security feature, and many administrators like to do that on Windows Servers, but that registry change will NOT apply automatically to Remote App implementation. And then, you are in a trouble . . . Server not listen on 3389, because you changed default RDP port, but Remote App configuration is not aware of new RDP port.
Fortunately, just one PowerShell command will resolve that problem and “inform” Remote App configuration about new RDP port.You need to new name of your collection and RDP port. For example, my parameters are Test Collection and port 45689.
Set-RDSessionCollectionConfiguration –CollectionName "Test Collection" –CustomRdpProperty "server port:i:45689"
Simple, is not it?