SIP-T46U no boot only RED MWI LED

[sysintegrate]

Hello,
i've got 12 brand new SIP-T46U from my Distributor,
i preconfgured them to the new Auerswald Commtrexx Business PBX.

After a reboot of the hole System (Cisco CBS250-48PP, PBX, all Phones) one Phone will not boot.
Only a RED LED Light on the MWI lights up, no display backlight, no sound - nothing.

All Phones are powered over PoE+, all the other phones doesnt show this error.

I think something in Boot process failed? Could i fix this? Or should i send this phone back?

I checked to press the + - Button to bring up a sound or longer press X to reboot the phone, without success.

Thanks,
Martin