Hi there,
We also ran into this exact issue, except we are going from UE 5.0.3 to 5.1, so it seems this issue was introduced in 5.1. If rendering preview level is off, everything looks fine in the editor. But once we turn on the rendering preview or package to our targets (we target Android and iOS) this issue manifests itself.
In the 5.1 release notes https://docs.unrealengine.com/5.1/en-US/unreal-engine-5.1-release-notes/ , there’s a bit saying:
Scene Capture render targets now start with the alpha channel disabled
Not sure what that means and if it’s related to this issue. We’ve fiddled with many settings to see if we can “enable” alpha again, but to no avail.