All versions lower than 18.104.22.168 are affected by this update procedure issue and the only available solution from such deadlock situation is to use the network recovery procedure as described in the Snom support How-to located here.
Important upgrade/downgrade instructions:
* Any phone running an 8.9.3.x or higher firmware should not be downgraded to a version below 22.214.171.124.
* This may lead to a deadlock situation where the firmware works, but the phone cannot be updated anymore at all!
* All versions lower than 126.96.36.199 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 188.8.131.52 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!