Soulframe uses UDP ports 4960 and 4965 (or whichever ports are set at the in-game options) in order to let you join games. If you have more than one PC playing Soulframe, these ports might conflict, and the second PC may be unable to communicate.
To fix this issue, change the network ports used by the second PC.
- Open the Main Menu (ESC on PC), select OPTIONS, then SYSTEM.
- Change the Network Ports [UDP] to another range of numbers (first PC/Console will be using 4960 and 4965 so pick another pair).