Export as positive copy tif issue

I was trying to use the export positive copy Tiff
My files are held on NAS, LR6
I selected a complete film (39 images) in LR by ctrl-A and then opened the export dialog box.
Export location set to a specific folder also on NAS and ticked the “add this to catalog” box.
Ticked “rename to” box, setting files to -positive.tif.
Image sizing and output sharpening left alone
Metadata - All metadata and ticked remove person and location info
No watermarking.
and the hit “export”

Top left export progress bar stated 39 images to export

Files started appearing in the folder (checked by a separate finder window) but the progress bar never moved. 25 images appeared in the directory but the progress bar never moved)
then a file named .afpdeleted3515172 appeared as a Tif image (104.7MB) then 2 more such files appeared and then tried to add these new images to the catalog and the first failed with cannot add image (or similar).
so, only 25 of the 39 images appeared in the directory and only the first was added in to the catalog.
Any idea what might have happened?

I can try this again if you want me to and record all actions in more detail. It took about half an hour to create the 25 tiff files…

I might be too ambitious with what I was trying to do and will try again by breaking the task into smaller steps.