Try these in the order listed:
- Close all Google Chrome windows and reopen Chrome; for both moderators and test participants. You can also put this in the url bar: chrome://restart
- Both moderators and participants run this test https://validately.com/moderated/systemcheck
- Make sure everyone is on the latest version of Chrome. Go to Chrome settings or put this in the url bar: chrome://settings/help
- Do a speed test to ensure that the participant is above 5 mbps upload speed: http://www.bandwidthplace.com. (works on mobile or desktop)
- Ask the test participant to remove the Validately Chrome extension. In Chrome, click Settings -> Tools -> Extensions -> Delete Validately (it may ask you to reinstall next time you take a test).