Are you using Unreal Engine 4? We no longer do origin rebasing in UE5. UE4 has been unsupported by Cesium for Unreal since April, so I highly recommend upgrading your project if you can.
If you must use UE4, you can turn off the rebasing with a checkbox on the CesiumGeoreference object, something along the lines of “Keep World Origin Near Camera” (I can’t remember the exact wording used in this obsolete version). But keep in mind that UE4 uses single-precision coordinates, so without rebasing you will have precision problems if you travel far from the origin.