Importing ICS Into Calendar - Some Entries Disappear

I am exporting my calendar from Outlook on my work calendar, and then mailing it to my MacBook Pro (macOS Sierra) so I can import it into my Apple calendar.

When I do so, here are two or three appointments that appear briefly, then disappear, leaving blank spaces on the calendar where they should be.

Looking for suggestions on what might be causing this. Thanks in advance...