The easiest solution is to not save your assembly as a custom door leaf (component) ... but as a custom door, since it seems that there is no aspect of the door object that you want to use?
View just your iron gate in 3D, then from Library menu, Save 3D As and save it as a door.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB