Netflix change their Thumbnails often

This is to get more clicks on the movies or shows.

Netflix say they have about 90 seconds to catch users attention before they move on. Your movie thumbnails will differ to another persons movie thumbnails, and that is because these thumbnails are based on what you like. The movies and shows you watch the most all play a part, like if you watch movies that have a certain actor in all of them, other movies that have that same actor will generate thumbnails with that actor in them. So you can click and watch them too, staying on the Netflix platform for longer.

Netflix uses Aesthetic Visual Analysis (AVA) to pick the best thumbnail to display to you, the user. It sifts through movies and shows to identify the best frames to use as thumbnails. Netflix has begun using a machine learning algorithm called Contextual Bandits to match thumbnails to each user in real-time.

Read more:
https://blogs.cornell.edu/info2040/2022/09/28/how-netflix-uses-matching-to-pick-the-best-thumbnail-for-you/#:~:text=Netflix%20uses%20Aesthetic%20Visual%20Analysis,frames%20to%20use%20as%20thumbnails.