Ubuntu 20.04 openconnect fails for GlobalProtect server

[O. William McClung]

I have openconnect v8.05-1, the latest for Ubuntu 20.04, and am trying
to connect to a GlobalProtect server which I know requires
gp-saml-gui.

$ gp-saml-gui -p -S --clientos=Windows <server> -- --authgr='US Central'

allows me to authenticate. After the long URL following this prompt

SAML login is required via REDIRECT to this URL:

comes

Enter login credentials
POST https://<server>/global-protect/getconfig.esp
8 gateway servers available:
 US Northwest (us-northwest-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com)
 US Southwest (us-southwest-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com)
 US West (us-west-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com)
 US East (us-east-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com)
 US Southeast (us-southeast-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com)
 US Central (us-central-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com)
 US Northeast (us-northeast-universi.gpo2ojjg5cnn.gw.gpcloudservice.com)
 US South (us-south-universi.gpo2ojjg5cnn.gw.gpcloudservice.com)
Please select GlobalProtect gateway.
POST https://us-central-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com/ssl-vpn/login.esp
Connected to 208.127.240.223:443
SSL negotiation with us-central-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com
Connected to HTTPS on us-central-g-universi.gpo2ojjg5cnn.gw.gpcloudservice.com
Failed to parse server response
Failed to obtain WebVPN cookie

Thanks for any help you can provide.

-Bill McClung