Unable to authenticate Perspective client

I have one user who is unable to authenticate through an IDP on a Perspective project. He has tried on different browsers.
He gets the following error in the gateway.

WebSocketChannel 31Aug2022 09:22:02 Websocket connection closed unexpectedly. code=1002, reason=Invalid UTF-8 in text frame, codeMeaning=Protocol error, codeDescription=The endpoint is terminating the connection due to a protocol error.
ClientSession 31Aug2022 09:22:02 WebSocket disconnected from session.
WebSocketChannel 31Aug2022 09:21:52 Websocket connection closed unexpectedly. code=1002, reason=Invalid UTF-8 in text frame, codeMeaning=Protocol error, codeDescription=The endpoint is terminating the connection due to a protocol error.

It continuously loops at the following:

Well, this is after authentication; this is the Perspective session attempting to start up.

Is there any middleware (firewall, port scanner, etc) between this computer and the gateway? If you look in the network tab in browser devtools while the attempt is made, does anything leap out at you? (You might need to click in to the websocket handshake to see the actual websocket messages).

Both sides seem to agree that there’s something weird in the data going back and forth.