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The teams and channels list is configured to run an update check and refresh every 60 seconds for European based costumers and every 10 minutes for American based costumers. How long the process takes depends on how many teams, channels and users are in the tenant and can vary between about 3-10 minutes. After adding a new channel refresh the page (from the refresh button of the browser) to see if it has been updated in the portal.
How to limit administrative access to teams
The compliance admin was not added to private channels. What should I do?
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Reactions to chats do not get moved.
Private Channels limitations
When a private channel is either the source channel or the destination, Wiki and OneNote will not be copied. The original channel will be kept so the content will not get lost. A message about that will be a part of auditing.
If there is no wiki in these channels, the behavior is like in public channels.