Thanks for the suggestion!
I only have a Pi Zero which I use to emulate Tube on my BBC Model B.
I tried formatting the card in the A3000 previously using !HFORM.
I still need to do a 'quick' FAT32 format on the SD card after writing the image back, before the A3000 will see the partitions on the card but some of the files are corrupted.
I should add that after a while, the A3000 stops seeing the partitions that it could access previously.
I have done this using different SD cards with the same outcome.
Perhaps this is an issue with the SD Card interface, which there are a lot of other threads about so I should probably post to one of those instead. My interface card has the FC1307A chip. I have ordered a CompactFlash interface so will post an update on a more appropriate thread when I have received and tried that approach.