Hello,
cannon seems to behave differently between BJS version 4.1 and 5.0
I have a physics controlled mesh (icosphere). This mesh has two child-meshes attached (blue boxes).
See this PG: Babylon.js Playground
With version 5.0 the blue box meshes seem to “sink” into the ground whereas with version 4.1 it behaves more as I would expect. I don’t think it’s related, but maybe it has something to do with a problem I’ve described here: Cannon physics undetermined behavior with HeightmapImpostor
Thanks for any help 
Adding @Cedric
There was an issue that was solved (i believe in 4.2) with compound meshes and cannon.js (and other engines as well, actually). It seems like this fix has a certain effect on meshes connected to a parent that has rotation prior to setting the physics impostors.
Try setting the rotation after creating the impostors and it will work as expected - physics version differences | Babylon.js Playground
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Thanks a lot @RaananW! Good to know, that did the trick