Structure Void blocks are breakable in survival mode

I placed some 'structure_void' blocks in my Minecraft Realm world in creative mode on my secondary account (on PC, by the way), then I switched to my main account and went into the world in survival mode (the platform is iOS) and I realized that I could break the Structure Void blocks, which I thought was impossible in survival mode. I’m not sure if being the Realm owner or also having placed 'Deny' blocks had anything to do with it, but that’s how it happened.