Hi @Hannah G
For our better research, please provide more information about this case:
- What is your account type?
- What's the version of your Outlook? Please make sure you have upgraded your Outlook to the latest version.
- Has the subject of the reply been changed?
Based on my tests, someone in Bcc doesn't affect the conversation view. If the subject of the reply is changed or the Show Messages from Other Folders option is not checked, it may affect the conversation view. The results of the test are as follows:
If the subject has not changed or other conditions affect the conversation view, please try the following steps to reset the view:
- Close Outlook, press the ‘Windows + R’ key on the keyboard.
- In the Run box, type in ‘Outlook /cleanviews’ and then click on OK.
- Using the command line switch ‘outlook /cleanviews’ will reset all views to default in Outlook.
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