This happens because the audio and video are sent in separate streams and if the bandwidth on the instructor or student side fluctuates it will create a slight separation of the of the streams.
If you are noticing that your audio and webcam video is slightly out of sync during your class there are a couple things you can do:
- When you turn on your webcam, there will be a list of settings to choose. Select "Low Latency Video" - This should solve your issue immediately
- Secondarily, connect your computer directly to the internet rather than using WiFi, or use a faster internet provider altogether