Very bad regression with AddInstance for HISMC in 4.19, wind gets reset for all existing instances

Theres a very bad bug in 4.19 and 4.20 with HISMCs.

This is 4.18:

This is 4.19:

The wind for all existing instances seems to get reset when a new instance is added in 4.19. I’ve also tested 4.20, and that has the same bug like 4.19.

Here’s the 4.19 project where I recorded the GIF with: HISMCTest419_.7z - Google Drive

To see the same, hit simulate in the TestMap level.

Actually, that HISMC bug is even worse. It does not just happen when you add a new instance, it also happens when you update any existing instance. So if you have a tree thats growing or something similar, all existing trees in that HISMC will get their wind reset.

There is a “fix” for this that “works”:

If there’s any static mesh existing and visible in the level with the same mesh like the HISMC, the issue does not appear.

Hello ,

Thank you for the report, this has been entered as Unreal Engine Issues and Bug Tracker (UE-61621)