I want to roll back the firmware version to 386.

[Tech9]

Sometimes it changes the file system and can't be rolled back (since the old firmware would not know that it has to change it back) other times it updates the bootloader and is no longer compatible with old versions.

I can't see this 386_43588 version (removed), but perhaps the reason is much simpler - it doesn't have V2 image file in it.