Keyframed object jumps instantly from one keyframe to next or not at all The body.001 is the object I'd like to animate but it moves suddenly from one keyframe to next, and sometimes doesn't even move at all when scrolling the timeline.

You can clearly see the timeline cursor at the beginning of animation:



And end:


But the object won't budge.

I've checked everything I can think of including:


Making sure all the keys are not straight lines in graph editor
Parenting to armature then animating
Deleting NLA tracks and again adding one
Not using NLA tracks at all and just using Action Editor


The body.001 can be appended to other blend files and animated without any issues
Your plane is a rigid body.

You need to check this button to allow it to be animated :



Edit : when you append it into another file, this file does not contains a rigid body world (see in the 'scene' panel). That's why the animation works in that case.