Hi Joshua Wyatt,
Welcome to our forum!
Does the issue occur recently in Outlook Desktop Client? Did you have any specific operation before the issue occurs?
What is the version of your Outlook? It is recommended that you please check the Outlook client version (File>Office Account>Product Information) and try to upgrade to the latest version to see if the problem is resolved.
To further confirm if the issue is more related with Outlook Desktop Client, it is suggested please log your account in to web version and do the same test to see if the issue persists.
If the issue persists, please check the permission by going to Right-click the group calendar>Properties>Permissions>Ensure you have sufficient permissions to access the calendar.
If not, you may disable Cached Exchange Mode in Outlook Desktop Client by going to File>Account Settings>Account Settings>Select the account>Change Account> More Settings>Advanced>Untick Use Cached Exchange Mode >OK>Finish and Close>Restart Outlook and then attempt to access your group vacation calendar again to see if the issue persists.
If it doesn’t work, considering data file corruption, it is recommended to create a new profile and re-add your account to it to see if the issue is resolved.
Hope it helps.
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