Two-Sided foliage materials with an Opacity of 0 ignore any shadows cast with Virtual Shadowmaps, even in a completely sealed environment. This did not happen in UE 5.1.1
1. Download the Licnesee's test project and open.
https://udn.unrealengine.com/s/contentdocument/069QP0000038whrYAA
2. Open the map /Game/NewMap
3. Observe the spheres are not being shadowed by the wall.
4. Open the Material Instance on them, /Game/NewMaterial_Inst, and increase the Opacity scalar parameter
5. Observe the spheres now are shadowed by the wall.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-204961 in the post.