Have you added port forwarding to your network? If so, try disabling it as that may be causing a problem since you set that up to forward to a specific IP address. With all the advances in routers over the years, you shouldn't need it other than as a troubleshooting tool (basically to bypass security that may be causing issues).

It's possible it could be a downed hop along your PC's route or something too. IDK the details on the PS3, but they may have done those clients similar to the PS2's. It may be something funky because of having to link into a server with Sony first, and then go on to SE's servers. Depending on just how it all works, it could result in different routing even though you are coming from the same modem.