Some DIgi one SP won't update Firmware

I have 3 Digi One SP having troubles when i Try to upgrade firmware.
Only those 3 items are affected.

Current Firmware Version : 82000774_Y
and trying to upgrade to 82000774_Z

I have the Following error message : FW_ERROR_INVALID_IMAGE
I also tried to redo the upgrade after factory reset, without any imporvements.

Any suggestion ?

What “POST” firmware are these devices running?