When Julian is talking to Erika, and tells her that Anneliese is missing, you can see a golden flower on his tie. But throughout the rest of the movie, and some seconds after you see it, it disappears.
Near the end of the movie as Erika's leaving on a horse she's wearing her old dress. When she returns she has the dress she borrowed on. No bag was shown attached to the horse's saddle for her to carry it in. Even if there was a bag the dress would have been too bulky to fit in it. Folding it wouldn't have helped.
During "To be a Princess", some items disappear and reappear between shots. The blue shoes Erika was wearing before switching them were next to the stool she was sitting on. They're gone after she stands up and walks forward.
The blue chair had disappeared and reappeared between those shots as well.
During the song "Free" Anneliese walks along her very long balcony whilst singing. A wide shot shows that she is halfway along the balcony, but then a shot after shows that she is only a few steps away from the edge, yet there has been no signs of her running or taking deliberately large steps.
Wolfie is a male calico cat. Calico cats are almost 100% female cats. In the very rare cases which there is a male calico cat it's due to a genetic disease and they are sterile so he couldn't reproduce with Serafina.
However, according to other sources, all but about one in three thousand could still produce kittens. Wolfie just wouldn't be able to produce a male calico kitten.
When Erika is playing as Annelise and is taking her bath, we see taps in the bath room. Plumbing would not have existed at that time.
Anneliese's mother says she missed her at breakfast, when Anneliese has breakfast in bed every morning.