If I understand correctly, you want your star to behave as a "billboard". There are lots of tutorials out there, one for example here: https://www.blendernation.com/2019/04/27/how-to-properly-billboard-sprites-particles-in-blender/
This tutorial shows essentially the method also described by @batFINGER, using the "locked track"-constraint....
One way to do this is with constraints. Namely the damped track and limit rotation constraints.
Here is how to do it:
First select your object and add a constraint, choose damped tracked from the drop down. In many cases, the axis will be -Z and in this case, our target will be the camera object.
Next, add a limit rotation, and tick both axes you wish to ...
Here is an example of doing this without operators.
Have the constrained object as active
Create a copy, strip the follow path constraints from it.
Create all the copies needed from the copy
Loop thru the copies,
calculate the frame,
set and keyframe offset based on frame
change to that frame
give the copy the same matrix world as ...
All constraints look for an armature and a bone. If you merged the "B" armature into the "A" armature, probably some constraint are looking for an "X" bone which was in the "B" armature, but now it is into the "A" armature. If all bones names are different, it should be enough to change all constraints ...
A bit weird answering my own question but I found a solution. : )
I now believe the problem was due to the piston and cylinder being each-others Damped Track target. I suspect micro translations of their origins when moving caused it, but that is a guess.
I added an object, child of the platform, at the location of the cylinder origin. And also an object, ...