Any entires added from the Banking screen will be deleted if unmatched, without warning.
I needed to separate some entires from a quickbooks account and relink the bank account to the new QB account. I could only unlink and relink by un-matching all entries. After doing this, I noticed that all entires I had made manually then matched were fine, but any that had been created by clicking "Add" from the Banking screen automatically got deleted, including all attachments. So now I have 200+ entries from the last few months to re-enter and find all the paper copies for to add as attachments.
This then makes me alarmed about the reliability of the record keeping in compliance with HMRC and therefore will resort back to keeping all paper records for 6 years.
Avoid using the "Add" function from the Banking screen!!!! Create the entry manually first, then use Match.