Trying to move one webinar in a recurring series creates time conflict

Hi there,

I have a series of 7 recurring webinars, however they aren't every week so I deleted the occurrences I didn't need. 

Now, I am trying to set one of the webinars from December 19th to 12th, but it's giving an error that the date/time conflicts with an existing occurrence. 

I looked in recently deleted webinars and there is nothing there, since it's been longer than 7 days.

Is there any way to fix this?