Whenever I initiate a call, it’s dropped with the error Server Unreachable. But subsequent calls pass through. Also, when someone calls me, the first call is always dropped. The problem existed with iode 6.x and still does with version 7.1.
You can find much information on the internet, it doesn’t seem to be related to Brax3, check that your APN settings are correct and if needed delete them and either reenter them or reboot the phone to let it update them by itself.
A good starting point is contacting your mobile carrier and explaining the issue. They have access to logs and can easily identify the issue.
There is no known bug with the BraX3 that causes the issue you shared. Causes for the issue can be different, including APN configuration, 4G/5G bands not supported by the device, and more.