I have recently discovered that I cannot use a folder with the word "lots" in the name (i.e., 'DownloadedLots', or 'StufffromLots' or just 'Lots'). The game won't (consistently?) read 'em. I renamed the folder to "BuildingsIwantstufffromdangit" (ok not really but something like that
) and it works fine now.
I actually seem to have been having issues with this since OFB or at least FFS, but I only just got around to actually figuring it out and fixing it.