Hi @Kiain ,
Please click the Junk E-mail folder in MFCMAPI, in the right panel, locate the PR_ATTR_HIDDEN property, check whether the value is the False.
If not, please double click it, uncheck Boolean option to change to False.
After that, please re-start Outlook to check this issue.
If issue persist, please do let me know and I'll do my best on continuing to help you.
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