Multiple instantiation of prefabs causes ambiguous IDs about stride HOT 3 OPEN

Easy to fix: do the fixup in your entity processor.

What is the actual use case of instantiating prefabs from within an entity processor? I don't think it should be done this way. It's not the purpose of an entity processor in my opinion. That should be better done with a script. The purpose of an entity processor is usually to gather associated data (such as sound instance, animation system, etc.), not to instantiate more entities or prefabs. What will happen if the prefab also contains the same custom component: it might create a recursive loop, with new entities being instantiated forever.

Note: I'm not saying there is no bug in this area. But I think more analysis should be done to understand the underlying issue and the consequence of any "fix". For instance, in the editor we have some flags to fixup ids when using the AssetCloner (see sources/assets/Stride.Core.Assets/AssetCloner.cs and sources/assets/Stride.Core.Assets/AssetClonerFlags.cs). The fact that it crashes in the editor indicates it tried to do some instantiation in the editor game which is not a supported behavior.

from stride.

The use case is that I want to create a generic environment, based on the settings in the EntityComponent, from combined prefabs at runtime.

My only known way to see this generic environment in game studio is to use an EntityProcessor. This is because, unlike ScriptComponents, it is also executed in the game studio.

Or are there other options?

from stride.

Right now there aren't, no. What you're trying to do is not yet supported, the editor builds a layer on top of the scene hierarchy that abstracts away a couple of things. It doesn't really expect new entities being spawned through user-code.
This is something that we should support in the future, likely after the editor rewrite, but right now your example is kind of outside supported behavior.
The underlying issue may not be though, if you can replicate this issue at runtime then we should definitely look into that.

from stride.