Hi Simon,
Welcome to Outlook IT Pro Discussions forum, In this case, you may need to clear the cache of TaskTask app and reinstall it and try again.
And here we mainly focus on general issues about Outlook desktop client. Since your issue may be related to TaskTask app, so if the issue persists, it is suggested to consult the team responsible for TaskTask app for more information.
Hope this can be helpful.
Regards,
Aidan Wang
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