I have an animated piece featuring a slow zoom within a clip. After some tweaking I finally got it to start and end slowly and smoothly - but with it came a kink at the end, where the position shifts much more suddenly. Here is the clip, and you can see the shift at :12 . This is a screen shot of Premiere for the clip.
Looking at that screen shot/Premiere, I can see that scale has a straight line when it changes values, while position has a curved line. I presume that difference is where the problem lies, but I'm not sure exactly what is wrong or how to fix it. I'll post any other info that is needed to explain the problem.
Select the Position keyframes, right-click, and select Spatial Interpolation > Linear.