Possible bug/glitch with Zed's ultimate.

At around 6:22 of the replay Zed uses his ultimate onto Syndra and she flashes away. However, the flash is resolved almost a whole second after the sound of flash and Zed's ultimate does something very weird. Both Zed and Syndra players claim that their game froze and lost control similar to an experience of a ping spike or package loss. Syndra regains control once the flash resolves. Attempted to recreate this possible bug/glitch (sorry for the lack of term knowledge) but failed all tries. Needs a better look from the eyes of a professional.