I cannot determine a pattern to the error, it seems like Outlook randomly chooses sent emails to not appear in my sent folder when searched for.
For example, despite emailing an individual multiple times over the past week, when I search their email or name in the sent folder, only the first email I sent appears. Sometimes when I search for an individual, despite emailing them several times, no emails appear.
If I scroll through the sent folder without using the search function and just use the "Filter" "Arrange By" and "Sort" features, the emails show. The issue seems to be solely with the search function.
This issue first appeared the last week of December. This is in an office and is affecting multiple deceives that use different emails addresses.
In trying to troubleshoot this issue, I found a common problem is the checkbox "Save copies of messages in the Sent Items folder" is left unchecked, for our issue this is not the case.