Your logs show two issues, the Initial connection failures (Network/Firewall) (client can't reach the server) and a session establishment failures (RDP/Profile) (Your client authenticates, but the session immediately ends).
As far as i recall this is not supported with the sandbox, the headend of the sandbox vpn does not allow the vpn to connect from a vm, one of the old threads showing this https://community.cisco.com/t5/devnet-sandbox/cannot-establish-vpn-to-devnet-environment/td-p/5128744
If you try and connect from your local machine to the sandbox does this work?
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