Really, that's not right, it should have been a dropbox folder that had public access so you should have been able to just drag and drop your images into the folder, you should not have to sign up or give any password, so dont do that at all, it certainly does not sound correct and not what I set up.
I have scanned in a A4 image at 1200 dpi, it is 126mb in size, that's the best I can scan, I assume its 8bit as I have no control over the scanner bit rate.
In DT I randomly applied some edits , base curve, filmic, tone curve, white balance colour correction
I then exported in TIFF uncompressed at 16bit. The export file size was 835mb and it took around 4 seconds
I then copied the input file to a new image 19 times and re-imported the new 19 images. Interestingly I had an error flash up about unable to allocate memory ????? export ???? they are the only words I managed to read before the error disappeared, no idea what the "export" part of the error message was about as I was importing at the time and waiting for the thumbnails to appear. They did appear after a couple of minutes, but one of the image thumbnails did not generate so out of interest I clicked this image and DT froze. A force stop was the only cure and on restart DT had lost all of the imports including the edit of the first image, interesting. Since then DT has exhibited strange behaviour, it crashed trying to reimport the images a second time so I suspect the catalog is now corrupt So its back to backups.
Now interestingly, I also have scanned Tiffs, maybe 8-10 thousand and at times have several thousand that I am working with at a time in the lightview display. However, mine are all scanned at 600 dpi so I am now wondering if there is a problem in DT with high dpi scanned images.
There is a section in DT options (cog icon) where you can adjust the memory that is used for certain tasks. Try playing around with them and see if it helps. Meanwhile I am going to restore my database from a backup lol