i downgraded ModemManager back to 1.6.8-2ubuntu1 and the problem went away, so it is caused by ModemManager.
attached are the logs for ModemManager 1.6.8-2ubuntu1
i downgraded ModemManager back to 1.6.8-2ubuntu1 and the problem went away, so it is caused by ModemManager.
attached are the logs for ModemManager 1.6.8-2ubuntu1