Missing Bezier handles for Position on value graph

The Transform/Repeater Position property does not display bezier handles for the position path. Unfortunately, you cannot open a Shape layer in the Layer panel, or you would be able to see the position keyframe paths. 

I suggest that you edit the Speed Graph instead. It is nearly impossible to edit a position path by using the Value Graph. If you cannot smooth out the position path using the Speed Graph

You could also try working with Keyframe Interpolation and Keyframe Velocity. 

The only other option would be to use the pen tool to draw the motion path you want, add a single keyframe to that motion path, then Copy or Cut it and paste the motion path to the Repeater/Position property. Then you need to add this expression to the Repeater/Position property:

value - [thisComp.width/2, thisComp.height/2]

You will get the precise path you want and rove over time keyframes, so you can adjust the timing by just dragging the last keyframe created.

Switch from "Edit Value Graph" to "Edit Speed Graph".

The bad news is that you're not alone and I have experienced the same problem. I hope that a solution presents itself soon.