Adobe Connect - Users Stuck in Waiting Room

We are using Adobe Connect with external clients. Some of our clients have tried to access our Adobe Connect classrooms. And while on the host/tutor side it looks like they are in the classroom, on the client side they are stuck in the meeting waiting room, as if they hadn't been admitted into the classroom.

We have sent the external clients the standard information (from Adobe Connect support page) on ensuring their firewalls allow Adobe Connect. The clients have passed this information on to their cybersecurity teams. The teams are adamant they have followed the instructrions but our clients continue to be stuck in the waiting room.

I am wondering if this is more than just a firewall issue. Has anyone else had this issue? And how has it been resolved?