Disappearance of "folder", but .pdfs still available in Groups

Hi, Within my Mendeley "Group" are numerous folders that are analogous to different projects. Within each project folder are sub-folders. Recently, I dragged a project folder with ~ 15 .pdfs to become a sub-folder of another project. Once I "synced", the sub-folder and corresponding .pdfs were no longer listed within this project folder. However, if I search for any of the ~15 specific .pdfs within the overall group, I can see the specified .pdf - but do not know where it's located. (a) I'm mystified as to how the sub-folder + .pdfs "disappeared". (b) Is there a way to identify the location (e.g. folder or sub-folder in Groups) of a .pdf once it's in view, perhaps via Details? Thank you!