Issues with Remote Desktop Web Client (HTML5)

Hey all,

I'm having a strange issue after implementing the Remote Desktop HTML 5 Client for one of our RDS instances. Everything is working up until the actual act of opening an application which we then receive the following error:

We have performed all of the verification steps to ensure that the set up is configured correctly and haven't had any issues out of other RDS instances with the same set up. Below is a list of everything that we have verified:

• The RDS server (singular server, running all RDS roles) is Server 2019 and is entirely up to date with Windows Updates.
• The public trusted certificates are configured correctly.
• Licensing is set to per-user client access, not device level.
• Verified that the RDS server's NPS is registered with Active Directory.
• Reviewed all appropriate connection and authorization access policies, verified that these are looking great.

We receive this error when attempting to access locally using the FQDN as well as externally over the internet as well. When performing a log capture we can see the following error:

2022-12-22T20:01:12.622Z WebSocketTransport(ERR): WebSocket error received for url=wss://removed.for.confidentiality:443/remoteDesktopGateway?CorId=%7B9ca382bc-96b8-444e-b22c-3e5cbc370000%7D&ConId=%7B299f9980-d47f-44e9-86e7-479750c95ab4%7D&ClGen=HTML%3D1&ClBld=Type%3DRdClient%3B%20Build%3Dprivate&AuthS=SSPI_NTLM
websockettransport.cpp(304): OnErrorFromJS()

Does anyone have any ideas or have ran into this issue before? The results online are very scarce and every recommendation that has worked for other doesn't appear to work in our case.

Assistance would be greatly appreciated!