Assuming that the firmware is fully up-to-date (912.30.11.61 as of time of writing), if an X912 still won't pull correctly into Control 4, it may be that the intercom hasn't automatically enabled itself for Control 4 operation
The following "hidden" AutoP commands can be used to force enable the Control4 communication. I've attached a .cfg file with the command(s) attached. The .cfg file can be uploaded in Maintenance -> Others -> Config -> Import. It is likely useful for other intercoms too. There are 2 commands because Akuvox has changed the format of the command so both are supplied just in case one doesn't work.
Config.DoorSetting.CONTROL4.Enable=1
Config.DoorSetting.Control4.Control4Enable=1
Additionally, it is worth ensuring that in C4, under Network, that the X912 has an IP Address set, this isn't automatically discovered within C4 so has to be manually set before the Web Interface username & password is set in Control4.
Furthermore, I've attached the current best C4 Driver and a PDF document on setting up group calling.