Adobe Photo Downloader causing problems

I have recently discovered that I lost upwards of 200 images whilst downloading from my camera. The loss was my own fault because of the way I have set up my workflow - i.e. after downloading I always reformat the memory cards - supposedly to keep everything tidy.

I am using Photoshop CS6, Bridge CC2019, and Adobe Camera Raw 9.1.1 along with Mac OS "Folder Actions" and a Nikon D750 - OK, I recognise that this is a strange hybrid - but that is the way it is:

Photoshop CS6: Use this because it is the last 'locally based' version - I do not wish to use Photoshop CC (I do not wish to have a monthly subscription!!)

Bridge CS6:  Can't use this because, even though it should, it doesn't recognise my Nikon D750

Bridge CC 2019: Recognises the D750 and is set up to run when the camera is connected - starts Adobe Photo Downloader where I can specify the destination format and folder(s) and kicks off Mac OS 'folder actions' to automatically route the downloaded images to where I want them (my image 'database'). Everything appears to run fine and the end result is I have one folder with jpegs, one folder with raw images, one 'backup' folder which has both the jpegs and raw files and a fourth empty folder. The first two folders and the last one are all in a folder which is named with "today's date". I always select 'delete camera images after download' - but, although Photo Downloader says that the images have been deleted - they NEVER ARE - they always continue to reside on the camera memory card. However, I can live with this - as said I format the memory cards after download.

Once the images are in my MacBook I can use either Bridge CS6 or Bridge CC 2019 - and both will start ACR 9.1.1 when opening an image - and ACR will use Photoshop CS6.

As I said - everything looks (looked?) fine - until my recent holiday - over three weeks I must have taken over a thousand photographs - including about 200 in the Norwegian fjords - I know there were 200 because when I have come to process them I have a gap of 200 in the file numbering - for both jpegs and raw images.

When I was downloading from the camera I realised that not all images were being transferred and analysis showed that a transfer was stopping after about 150 images (actually varying between 140 and 160) - this equated to 75 jpegs and 75 raw images. Realised that Photo Downloader was only "finding" the 150 images - so was actually downloading everything that it found. For a short while I tried downloading the +\-150 images then deleting those from the camera and repeating the process - but this was too cumbersome so eventually gave in and used Nikon ViewNX-i to do the transfer. Unfortunately it looks as though, during that 'download/delete/repeat' process I inadvertently deleted 200 jpegs and 200 matching raw files

So, after all that - has anyone any idea why Adobe Photo Downloader would fail to see ALL the images on the two memory cards - with more or less the same quantity selected from each memory card?