After downgrading the phone from 8.9.3.x to a version prior of 22.214.171.124 the phone is not able to perform any upgrade / downgrade.
The visible symptom is that after applying the firmware upgrade from the web interface the phone just reboots, the normal update procedure doesn't start, and at the end of the boot-up the phone shows a "Firmware update failed" error.
- Any phone running an 8.9.3.x or higher firmware should not be downgraded to a version below 126.96.36.199.
- This may lead to a deadlock situation where the firmware works, but the phone cannot be updated anymore at all except for a network recovery.
- All versions lower than 188.8.131.52 are affected by this update procedure issue.
- Only option left to get out from such deadlock situation is to use the network recovery procedure as described in our support How-to
- If the downgrade is mandatory, use the 184.108.40.206 as an intermediate firmware downgrade step, before you finally install the desired/known as affected version!
- Please note: if you experience the deadlock situation do not open an RMA case, as this is not a hardware/flash issue. The phone can be recovered via a network recovery.