Thumbnails in TIFF file export

Hi, I love DxO PhotoLab. Just one problem though. When I export a TIFF file I find it will not upload to my favorite lab for printing, namely WhiteWall in Germany. WhiteWall’s website indicates that the file is defective, and will not allow the upload. When I inspect the TIFF file with Preview (on a Mac) I see two pages displayed–the main image on one page and a tiny thumbnail on another page. My workaround has been to open the TIFF file in Affinity Photo and re-export it as a new TIFF file. The newly created TIFF file does not have an embedded thumbnail, and the image displays as a single page in Preview. Furthermore, this TIFF file does upload successfully to WhiteWall. So, maybe WhiteWall can revise their facility. But on the other hand, from my end, I’d rather not export a file from PhotoLab that contains a thumbnail to begin with. I can’t find any way in PhotoLab to turn off the production of the thumbnail. Is there any way to solve this problem? Thanks, Joan