Hi! What our lab engineers seem to notice is that you are using G729. Please check that you have it installed on both sides. You can check this under Admin > Add-Ons > Add-Ons.
Next, would you be able to send Screenshots from the Asterisk Console (from where you are placing the test) at the moment you are running the test? For this you would need to have two PuTTY Sessions opened to the machine. One to run the Test, the other to check the Asterisk console (asterisk -rvvvvvvvvvvvvvvvvvvvvv).