Examined the events in your Google Calendar that were from your Outlook share/import? Is there anything different about them compared to an event that you created manually directly in your Google Calendar?

If not, them I am sorry, but I don't know of any reason why it would fail to sync events, that are in your Google calendar, just because they came from an Outlook Calendar share/import.

You might want to try posting your question on the Google Calendar Forum
Google Calendar Community