My guess, as the gray boxes are indicative of the data folder being in the wrong place, would be you have nested folders somewhere
Example
if the Path Should be Studio/Content/data
and you have it installed at Studio/Content/Content/data
or even at Studio/Content/data/data
then the second nested folder will mess up the paths, and while the items may show up in Daz Studio via the content library or smart content, the nested Content or data folder in the latter instances would prevent the items from loading as the .duf will be saying the files are in Content/Data while the files are actually in Content/Content/Data or Content/data/data so when Daz Studio looks in Content/Data it will not find the files.
Daz Studio is set up to be very flexible with the libraries with the exceptions of the data and Runtime/Textures folders, it expects them to be more at root level for the particular Content Directory so in my example the root folder is Content so Daz Studio expects to find the Data folder in the Content Folder. So whatever your root folder is set to whether it is Content, My Library, My Daz 3D Library, 3rd Party Stuff, or Bob, in that folder is where Daz Studio expects the data folder to be, and if it is not there, it will cause a failure to load, which when dealing with the mesh or geometry items in the scene causes a gray box or collection of gray boxes to appear in place of the mesh.
Hope this helps
P.S. I'm using the old format of the Studio/Content as that is how I have things set up on my external drive. I know the more recent paths are usually to the users/public/documents/My Daz 3d Library/ or users/public/documents/My Library/ or similar set ups.