Flashing fails with SDHCI error

Our Drive PX2 Tegras stopped working after some car testing. Nothing comes up through the HDMI ports for Tegra A or B. The Aurix console is accessible. We tried flashing the Tegras from DriveInstall (Ubuntu 16.04 host), but get errors like the following:

Erasing eMMC(3460000.sdhci) …Command Failed: /tmp/nvdd --device /dev/block/3460000.sdhci -E eoffset=0,esize=0
nvdd: /dev/block/3460000.sdhci not found, looking by controller instance…Device not found /dev/block/3460000.sdhci
Error Code 0x30011
Cannot open device /dev/block/3460000.sdhci
Error Code 0x30011
NvddGetDeviceInfo failed
Error Code 0x30011


Has anybody run across this problem?