Keyframes jumping all over the place?

Hi,
So I parented a group of objects to an empty.
I key frame the empty to move across the Y axis in a linear fashion, using only 2 keyframes across 250 frames (1st keyframe at frame 1, 2nd and last keyframe at frame 250).
First keyframe is at a position of 0,0,0 2nd is at a position of 0,-145,0 however when i step back one frame from the last keyframe the position of the empty jumps to 0,-115,0, and the next keyframe (the last one), which was supposed to be 0,-145,0 now becomes 0,-120,0.

Is this a bug or what is the matter?

All my objects have their transforms applied prior to animation, and the interpolation is set to linear.

Hi,
what do you see in the graph editor ? can you post a screenshot ?

hey, sorry i didnt reply. Been busy with this project as my deadline is around, the problem is still there.
I took a video to show it better
Jumping Keyframes Video

Seems like you’re doing things right. Can you share a stripped version of your file ? (only problematic objects)