my wild guess is some component can’t do tcp and does udp only (turnserver?)
Tor, the underlying tech for the AP hide-my-ip feature (not a vpn), doesn’t carry UDP, it’s TCP only (there are spec proposals for tunneled UDP over TCP though).
So WebRTC, what Talk is using, needs to fall back to TCP for everything it does if udp is detected to be unavailable. Admins of the talk-hpb instance maybe didn’t expect users with no udp?
(on another note: enabling Tor on any network route negatively impacts latency, not something I’d do to voice communication)