There are times that when a cover is arranged, these would need to be cancelled. This can be done by going on School > All Staff > Cover.
Once on the page, click on the arranged section so that you can view all of the arranged covers.
To then cancel any of the arranged covers, tick the covers that are getting cancelled. Click on the Bulk action button and select Un-arrange (Cancel Cover Arrangement).
The lessons will then populate in the Unarranged tab due to the cancelled cover.