I noticed IPV6 support is erratic. In some networks, even thou there is an available ipv6 route to my home server (I can attest it by connecting to windows RDP using my ipv6 address), Parsec seems to try only the IPV4 route resulting in error.
I would go for an option to manually enforce the use of IPV6:
Users are either on regular connections (therefore ipv4 or ipv6 will do);
Or they are under CGNat, where IPV6 is the only option.