Flipped image. Near the end, Ida is resting in bed with her head on a pillow, to the left side of the screen. The close up shot is from above looking down and the image is flipped. A small mole that has been on her right cheek throughout the film is, in this shot, on her left side, and returns to her right side in the following shots.
When Ida is in a church, the priest seems to be getting ready to say Mass and we see a versus populum altar, which didn't become the norm until years later after Vatican II. The movie takes place in 1961 and the priest would have been saying Mass on the high altar.
The sound of the car is wrong. For example, when Wanda starts the car in front of the monastery and drives away, the sound of a four-stroke engine can clearly be heard. However, the car is a Wartburg 311, which was built only with two-stroke engine.