I just wasted a full day with trial and error to understand that entities are not bound to the current active scene and will not get unloaded when I do a hard reset on the scene (loading the same scene in single mode).
Also BlobAssets are not unloaded and there seems to be no automatic way to set this up - so I had to keep a reference to all the Colliders I create at runtime (which are Blob Assets) and Dispose() them before reloading the scene.
Also I had to destroy all the Entities I create at runtime before reloading.
Also the SystemBase won’t get destroyed on scene reload, the OnDestroy() method is never called.
ECS Team, please add this to the documentation. These a crucial concepts. The one with the Blob Assets is actually documented in the BlobAsset-Documentation but it is not mentioned in the Unity Physics Documentation where it is required.