Barnaby's cummerbund/sash was not only badly tied, it appears full under, and partly under his tunic as well as correctly over it at various times.
Barnaby orders Winter to check if there were cameras on the medical supply drones. Since drones are piloted remotely, by default they would have cameras.
A drone that runs on GPS would be able to fly on its own without being steered. But then again, GPS is often not precise due to 9/11 security features built in.
Coroners are not ballistics experts and would not be making any statements about high-velocity bullets.
Mrs. Oswood's long pincurls are a different color than the rest of her hair.
When DCI John Barnaby talks to the lady-owner of the Jane Austen Tea Room, he checks the visitors book. Two persons gave their address as "Causton - Midsummer".
No one would store expensive drones on shelves and tables in a roofless landing zone structure in a country with as much annual rainfall as Britain.
In order to fly drones in the UK, a person must register, pass a test, and get an operator's ID. The criminal record of the young man in the medical drone office may mean they are flying drones illegally.