Many years ago, Tesco Polska did a study on the impact of placing a standard product (Tesco brand soap) at a standard price in the promotional area. It turned out that sales increased because customers often work on the so-called auto-pilot, or patterns fixed at the subconscious level "products in this place, are always at promotional prices".
In Lidl probably a mistake occurred, because the shrimp from the photo were in 2 freezers (mistake No. 1), separated from each other by about 4 m. The price was identical, but once it was great deal (mistake No. 2) accented with a large orange pricelist ( simple and effective POSM), and the second time the price of PLN 29.99 was the standard price. Sales have definitely increased, but a bit by chance. To conclude - retailers must watch over the promotion update (which is not easy on this scale), and customers should be more vigilant.
It is also worth carrying out regular verification in stores using modern tools based on "image recognition" such as Pro.Display.