com.apple.ImageCapture error -9934 is real. How do I fix it?

Scenario;

Transferring photos and video using ImageCapture v8.0 from iPhone 11 Pro running iOS v14.71 to a mac pro running OSX Big Sur v11.5.2 connected by a genuine apple USB cable. ImageCapture converts the photos from HEIC format to JPG in Pictures/Adriani11

Problem;

Some photos consistently fail to transfer. I get a pop up error window that says

The operation couldn't be completed.

(co.apple.ImageCapture error -9934.) (-9934)

(null) IMG_2813.JPG

IMG_2789.JPG

IMG_2760.JPG

IMG_2281.JPG

This has occurred several times now. Previously I've worked round the problem by AirDropping the troublesome photos. But its getting tedious and needs fixing.

Things I've tried to fix it;

1) checked disk space and permissions on the target folder. 45Gbyte of free disk space and Read/Write access so no problems there.

2) tried using a different account on the same mac pro. All photos transferred into JPG OK

3) tried using a different iMac. All photos transferred but remained in HEIC format

4) Restart the iPhone.

5) Read all the other support posts I can find about the -9934 error. Seems lots of people have the problem but no-one has fixed it :-(

Questions;

1) As the photos all transfer OK using a different account, a different computer and AirDrop, this implies that the photos on the iPhone are all OK. So what is it about my account settings that is fouled up?

2) Why does ImageCapture on the mac pro transfer into JPG format whilst on the iMac it retains the HEIC format? I can't find an option setting for this anywhere.

Thanks

Adrian