De-register the 300Wx

In the settings menu of the 300Wx you set CAT-IQ to disabled

Restart the unit

Now re-register

If this doesn't help you can downgrade the DECT module firmware to 935.

Downgrade DECT module firmware 
This is sometimes needed to improve interoperability. 

Follow the steps below to upgrade the DECT firmware in Konftel 300Wx.

  1. Make sure you have latest application version in the Konftel 300Wx before you upgrade the DECT module
  2. Download version 935 of the DECT module
  3. Place it in the root of a SD card.
  4. Insert the SD card in to the Konftel 300Wx
  5. Go to MENU (gear) > Settings > Upgrade mode and select DECT
  6. Progress dots will be shown on the screen during the upgrade which will take approximately 3 minutes. "SUCCESS" shall be shown on the screen when finished. 
  7. Restart the Konftel 300Wx. It is now ready for normal operation.
  8. Verify the DECT firmware version in the MENU > STATUS menu. Cycle with the arrow keys to get more information.