How do you downgrade firmware on a Ruckus 7150 switch?

I have several Ruckus ICX-7150-C12P switches, and I'm having some issues with ports disappearing, or general stability:

https://www.reddit.com/r/networking/comments/bfxsd6/ruckus_7150_port_always_goes_down_2_minutes_after/

It's currently running 08.0.90a - but somebody pointed out the recommended current release is 08.0.70d - so I thought perhaps downgrading to that version might help.

However, I can't seem to downgrade via USB. Copying over the primary flash works:

ICX7150-C12 Router#copy disk0 flash SPR08070d.bin primary 

ICX7150-C12 Router#Load to buffer (8192 bytes per dot) ............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ SYNCING IMAGE TO FLASH. DO NOT SWITCH OVER OR POWER DOWN THE UNIT(65536 bytes per dot)... .................................................................................................................................................................................................................................................................................................................................................................................................................................................................. Copy Done.

However, when I then try to copy the bootloader, I get an error:

ICX7150-C12 Router#copy disk0 flash mnz10114.bin bootrom 

Invalid input -> bootrom Type ? for a list

It would seem bootrom is no longer a valid option?

ICX7150-C12 Router#copy disk0 flash mnz10114.bin 

client-certificate client RSA certificate client-private-key client RSA private key file Copy file to flash fips-primary-sig Primary signature file fips-secondary-sig Secondary signature file fips-ufi-primary-sig Primary ufi signature file fips-ufi-secondary-sig Secondary ufi signature file local-pri Primary code image on the local unit local-sec Secondary code image on the local unit primary Primary code image secondary Secondary code image trust-certificate SSL Trust certificate

Is this related to my moving to a UFI firmware image?

If so, how can I safely downgrade to 08.0.70d?