If you believe you are missing emails, they could have ended up in Office 365’s quarantine.  Microsoft has increased its efforts to mitigate spam and phishing threats, and this has resulted in a larger number of false positives.  To check your personal quarantine, by going to https://protection.office.com/quarantine.  Here you will see a list of emails that are being held in quarantine.  If you select a single message the details panel opens and allows you to act on the message.  If you are confident the message is legitimate you can release the message and it will be in your inbox shortly.  If you are unsure, you can preview the message before releasing it to your inbox.  You can also submit the message to Microsoft and let them know the message should have not been blocked.   If there are several emails that you want to release, you can select them all and click release messages.  You will be given the opportunity to report the messages to Microsoft for analysis and release them all at once.