Apache Guacamole Connection Issue to VM (ERROR_TUNNEL_303)

We are using the Apache Guacamole 1.3.0 in AKS with with containers for ngnix, guacamole(client) and guacd(server).

User has been using the Gucamole to connect to the VM for months but recently user is getting the error message in Gucamole as below:
Error: "You do not have permission to access this connection. If you require access, please ask your system administrator to add you the list of allowed users, or check your system settings."

This is an error "ERROR_TUNNEL_303".

Note: There were no configurational changes made to the guacamole client or server while User's VM was being utilized.

No changes to VM, no changes in guacamole client or server were done at any time.

It will be greatly helpful to understand why we are getting this error or what could cause such an error.

Could anyone respond to the above issue if they got any leads or has faced similar issue in their past. Open to your suggestions