I've noticed the same. When I am travelling, I always use my VPN for access to company, bank etc so leave it on all the time. On occasion when I have been following something interesting, I've tried to access Prune but it never works. To access, I have to log out of my VPN. Not the biggest tech problem in the world but I presumed IB have someone who spends their time blocking VPN IP addresses for advertising statistics reasons.