best response confirmed by ThereseSolimeno (Microsoft)
Solution

@bwalker2020 There are a number of reasons. This can be a results of students connectivity, if roles are not setup correctly other students can remove meeting participants.   Please work with support if this is a systematic challenge as well your admins can see the users issues in the Teams Admin Center under Call Analytics for each user's calls. https://docs.microsoft.com/en-us/microsoftteams/use-call-analytics-to-troubleshoot-poor-call-quality

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