Can't play friend match

Went normally until character selection, but then once I picked my character the opponent’s cursor stopped moving. When we retried, we both found we were moving on our own end, but the opponent’s cursor wasn’t responding. Around then, key input stopped responding on the character select screen. We both agreed to close the game, then I entered practice mode. The controller setting said P1, but it controlled P2, and I couldn’t progress through the game. Even if I disconnected the controller, it didn’t fix it.

I don’t know my opponent’s (Sumeragi’s) computer specs (probably very good).

Mine: Fujitsu Lifebook AH53M w/ Intel i7 (C&D drive is about 50% used). Internet connection through au LTE tethering (Could this be the cause? But it worked fine on the Patreon build.)

Controllers: Both players used Xbox 360 controllers.

Other notes:
• It took a long time for the opening screen to come up! It felt like loading was really slow.
• Animations were too slow
• On the character select screen, characters appeared well after their names showed up.

Screen resolution 1024×576, full screen off, graphics set to lowest, and vsync off. No problems in practice mode.