Told you 😉
Incidentally that is where the initial release of the BMS Manual is incorrect. It should have said port forwarding for IVC Clients is no longer necessary, but IVC Hosts will still need to forward the ports. However, as you have found, some routers do still need to have the ports forwarded, even for clients.
The next version of the Manual will probably just recommend everyone forwards UDP ports 2934 & 2935 for BMS and 9987, 9988 & 9989 for IVC. Once you have set up port forwarding on your router and set up DHCP Reservation to make sure that your BMS PC’s internal IP address doesn’t change, you shouldn’t need to touch those settings again.