Idk if the problem is still actual, but I faced this problem too literally today.
The solution is You need to keep the path to the file that is set in your downloaded uassets.
for an example:
-You downloaded the assets of a character or location or something else and you should have a Content folder inside it.
-You have to copy ALL the files from Content folder to your own Content folder, and not to any other folders.
It happens because all the uasset files are connected with each other, and moving the files between them may cause issues. I hope I helped you