Problem with gaps between hierarchical instanced static meshes


I am experimenting with landscape from static meshes. First I create it from static mesh actors and then using the widget utility I convert it to one actor with static mesh HISM components… but for some reason, gaps appear between instances. I do not understand how this is possible - i just take actor transform and use “add instance world space” (Before conversion to instances, there are no gaps between the actors). Maybe someone knows what could be the problem?

This is probably related to the precision issue with HISM. Here’s a bug report I filed last year: Unreal Engine Issues and Bug Tracker (UE-81897)

There are numerous other related bug reports about strange HISM offsets that seem related to precision inaccuracy.

Yes … the instances are slightly reduced in size - it looks like I have to increase the size a little by 1.00065. This is a pretty bad decision, but the cracks are no longer visible.