Ella's first response to Wallander on the dating site indicates that he had previously sent her a message, which is not shown. Her response roughly translated reads: "Thank you for your nice letter. I agree that summer can be felt slowly when you can not share it with anyone. There's something I like about your attitude. Get out here if you happen to be free anytime soon."
Wallander's mobile phone changes phone language several times during the film, from english to swedish, and the other way around.
When Kurt looks at the dating website which his daughter signed him up for, his profile page gives his height as '1.88 cm', which is about three-quarters of an inch. Presumably they meant either '1.88 m' or '188 cm', which would be just over 6 feet (and a few inches taller than Branagh actually is).
When the medical examiner first uncovers the corpse of the supposed heart attack victim in the morgue, the corpse's eye is twitching.
The second message Kurt receives on the dating website from Ella is exactly the same as the first, down to the date and time. However, when he reads it aloud in English the words are completely different than those shown (in Swedish) on the screen.
The murdered taxi driver's bloody ID card reads "Johan Lundberg," but later when Wallander later refers to him on the phone, he calls him "Gunnar" Lundberg.