Cant see Local Data With Cesium for unreal when disconnect network

i had load loacldata by file:///+.json and its useful in edit with network,but when i packed the project and Disconnect network,i cant see anything both project and unrealengine edit;

so,is there must connenct network for cesium for unreal?

What do you see in the Unreal console log?

Any errors or helpful info?