Issue Importing ICS Calendar File to iphone

I have several calendars that I have “saved” as ICS files from my outlook. I have been successful importing all the calendars, with the exception of one, by emailing myself the file, opening the email and then opening the attachment. Once I see the list of entries I tap on Add All and choose the calendar to add them to on my iPhone. However, when I try to add the last ICS file, I only see a list of about 1897 entries all the same...

“Ends New Event” (see pic)

anyone have this issue before? Possible solution?

thanks

microsoft outlook 2016 pc version

iphone 7 Plus iOS 12.1.3