This is the wrong Software version for this platform. ASR-920-12SZ-A will have an igp in the software version name. Such as asr920igp-universalk9.17.09.02a.SPA.bin or asr920igp-universalk9_npe.16.11.01c.SPA.bin.
In your set values you will see:DISABLE_SD_FLASH=yes
To set an environment variable for the primary flash you have to specify "-p". For example:
switch: set -p DISABLE_SD_FLASH no
This should work for you. Env variable will then show as:
DISABLE_SD_F...
