Have you only got the props seen from a distance set to HLOD and all the little stuff not in HLOD ?
In the Build menu, do a Build Landscape first, then do Build HLODs but delete HLODs first before you build HLODs, hopefully it does something.
Ignore all the thousands of Yellow Warnings in Build Landscape results, filter them out with the drop down menu at the bottom and see if there are any red errors.