exporting folders

I have been exporting photos from my Aperture Managed library to a General Referenced Folder as part of moving into Lightroom.

I notice that after importing into LR, in Pictures, where the exported folders/photos are filed, the image of the photos disappears, just leaving a blue folder with a name but no thumbnail image when I click into the folder. It is there before I import into LR.

Will this create an adverse issue along the line?

Should the thumbnail image of the photo always appear?

Appears the photos have been imported in LR ok.

Grateful for any knowledge on this issue.

thanks

john