Hi and thank you for your reply,
I have already reflashed the latest firmware twice and none of the disk reports any physical or logical error (SMART, HDTune, CHKDSK)
If I recall this correctly, this mischievous error appeared on another set of mechanical drives on a firmware upgrade a couple of revisions ago. One day the "Initializing Devices" worked as intended but on the next cold boot, the boot process halted on "Initializing Devices"