Hello James,
Thanks for reaching out and I’m sorry you are having this issue.
What happens is that when you delete an imported event, it still remains in the database, only hidden, so the importer will not import it again. There’s a workaround / snippet for this.
Please check this thread where the issue came up. You will find the solution and the snippet there in the beginning:
Recurrent imports not working (google calendar)?
Please let me know if this helps or is you have any other questions.
Cheers,
Andras