iDRAC vFlash Does not Create Partition from Image

• Sometimes fail almost immediately with error: RAC0237: An error occurred while uploading the vFlash image.
• Sometimes it runs for a while (e.g.: 18%, 24% etc.) then seems to stall as it doesn't progress any further with no errors
• Sometimes it runs for a while (e.g.: 18%, 24% etc.) then fails with error: RAC0235: vFlash image upload timed out.

racadm -r 192.128.100.100 -u root -p calvin vflashpartition create -i 1 -o Drive1 -e cddvd -t image -l //192.168.100.10/iso$/sli.iso -u blah -p blah

Partition image upload in progress. Depending on network speed and traffic,
large image files (3-4GB) may take more than 1 hour to complete. To avoid
data corruption, please do not interrupt the upload or reset the iDRAC.

racadm -r 192.168.100.100 -u root -p calvin vflashpartition status -i 1

ERROR: Partition 1 does not exist.

racadm -r 192.168.100.100 -u root -p calvin vflashpartition list

No vFlash partitions currently exist.

• iDRAC version is 2.70.70.70
• vFlash SD card is not write protected
• vFlash SD card health is 'OK'
• vFlash is indeed enabled 
• Am trying with the Dell Support Live Image (SLI) but plan to do this with Server 2019 and other known-good ISO's.
• I am doing this remotely but on the same LAN; it's right next to me connected to the same switch as my management machine