I switched my event video. Do I have to re-enter chats?
Unfortunately, yes. Chat Replay messages are assigned on a timeline, when a new video is uploaded, these timestamps will no longer match. So chat replay will need to be revised to suit the new video's timeline.
This something that can easily be done in Chat section's Bulk Operations download to adjust .csv file at your end & reupload.
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Can I change my webinar video without starting a new event? (switch video)