Hi,
Can you see the emails if we check them in OWA?
Have you tried resetting views for the user in Outlook in case these emails are hidden by filters? To do this, exit Outlook, press Windows key + R to open the Run command, type
outlook /cleanviews and press Enter.
Please also hover the mouse over an email message in the search result, and see which folder the email is currently in:

Besides, please also check whether there is any rule set in Outlook which could move the emails to other folders.
Regards,
Steve Fan
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