Currently, Get Constraint Force node doesn’t include force of the linear drive. What seams to be returned is only the forces which are applied to keep joint in place.
I’ve made a simple test scene to demonstrate the issue. If you switch off the linear drive you can see that magnitude of force at Z is roughly equal mass * 980. Without a complete constraint force is rather hard to calculate a load on an element if constraint is used as suspension.
Test scene:
just a sidenote, not a fix…
There may be a flag that needs to get set so drive constriants will writeback their force, also, a temporary workaround might be possible by just using the displacement distance from the target position (since force is proportional to length-restlength.
some more details in discussion here: Linear Position Drive and Constraint Forces - World Creation - Epic Developer Community Forums