Unwanted movement between keyframes

[Shivam5C68]

I am trying to make a very simple movement of a line from point A to point B. But there is unwanted movement between keyframes. There are no keyframes in between yet it is moving. I have attached screenshot of the timeline as well as the video. Please help. 

Also, when I try to do spatial interpolation - linear, my spatial interpolation option is greyed out, 

Please help. Urgent!! 

[Mylenium]

Of course there's no spatial intzerpolation. Those are 1D properties. All that matters is temporal interpolation, so you need to change that. In any case, you may want to study the online help on some basics, including how to tweak such stuff with the graph editor.

https://helpx.adobe.com/after-effects/using/keyframe-interpolation.html

Mylenium

[Shivam5C68]

Thankyou for replying. I have set temporal interpolation to linear. Still it is moving. Can you help me solve this issue. I request you to watch the video if you don't understand my problem. 

I am even attaching the graph below.

[ShiveringCactus]

I think what's happening here is that by animating both the start and end properties at the same time, you're effectively changing the length of the blob so that it appears to move backwards.

It might be simpler to set the lengths for Start and End and keyframe the offset instead.

[Andrew Yoole]

I agree with Shivering Cactus.  The issue here is you're simultaneously changing your start and end points, resulting in a confusing length change in your animated line.  Using offset is a more effective way to animate this, or otherwise animate your end point first, then change your start point to match.  Typically your start point will need to begin animating a few frames after your end point does to maintain uniform size.