Static meshes in Procedural Foliage Spawner not blocking?

Hoping someone can help me.

I am building a forest with the procedural foliage spawner and for some reason, although I have ensured all of my tree meshes’ collision presets are set to “block all” my character can run straight through them as if they weren’t there. If I set the spawner to block all, the character can’t enter the space at all.

Using 4.27. Can anyone tell me what I am missing? Ta.