https://github.com/mongodb/mongo/blob/53adeef7dbf5170a94f3e6d25425e8524fb9d062/src/mongo/db/s/collection_metadata.cpp#L104

getOwned() here does nothing to the object being called.
It only returns a new copy.
it is unproper used, and may lead to bad memory reference.
Perhaps metadata->_keyPattern = this->_keyPattern.getOwned() is what you need.