"Video jitter is the amount of variation in packet delay" - in other words, data packets are expected to arrive at their destination at regular intervals and jitter is the amount that the arrival time differs over a given time period.
Jitter can be caused by packet loss and network congestion - both of which are often the result of a bad wifi connection.
If while in a Sessionwire session the Video Jitter warning appears repeatedly and a Wi-Fi connection is being used, switch to an ethernet connection instead, with Wi-Fi turned off.