Slit slider animation curve, how to fix?

Question

3D

Hello.
I decided to install a slider in the header of the site called Slit. I've used it before and had no problems. I understand that the fault is completely on me, but I can not understand what's wrong.
I checked it locally beforehand, inserted the necessary text and photos, adjusted it to size, everything seemed to be fine. But when switching to the next slide, the current one abruptly shifts down before the animation starts.
I am not strong in javasctipt, so I could not figure out how to solve this problem (or turn it off).
Also, if possible, how can you fix the "accuracy" of elements when loading the script itself?
Website