I don't have time to rewatch right now, so I'll just ask: is it definitely a teleportation problem, or might it also be that he couldn't help because he wouldn't know it was happening?
It might be just the latter, but if it were, surely he could just fabricate some sort of engagement that took all of Professor Shen's weekend and then portal in as the Envoy and punch Zhu Jiu's face without the need for a road trip? (Since it seems he was forced to make it into a research trip because he needed someone to drive him there, and xiao-Quan had a driver's licence.) The subs at least didn't state explicitly.

(How does Shen Wei figure out when to appear, anyway? It's not like the SID lights up a batsignal...)