Forwarding calls from one auto attendant to another and then to an external number

I am trying to set up call forwarding across multiple auto attendants and then to an external number.

We run a boarding school and have a main number that all calls go come in on. People can then choose which area they need to be redirected to, for example to one of our schools. Because we have schools at multiple locations, if they choose to be redirected to a school, they also need to pick which one.

The way I have this set up is that the main number is an auto attendant that lets the caller pick from a number of options. Some options redirect to an external number, some to a second other auto attendants.

All the redirects from the main auto attendant work, also those to external numbers. However, the redirects that first go to another auto attendants and then to an external number don't work. They simply ring once, then stop ringing, but the line stays on until you hang up.

I have checked the licensing and resource accounts, they are all set up correctly, I even had our external parter double check this.

Has anyone experienced similar issues? I am thinking that it might just be that redirecting through multiple auto attendants is not supported, but this would shock me as it's a feature required by a lot of businesses.