Odd MM Bearer behavior

[Christopher Penney]

Hello, I'm reaching out to this group in desperation.
We've been trying to solve this problem with ModemManager and a specific
SIM from IoTDataWorks combined with ModemManager inside BalenaOS that has
us perplexed and stuck.

We've tested this SIM which uses T-Mobile under the hood on other devices
and it works fine.  The issue is when configuring it for ModemManager on
Balena.  In particular mmcli -m 0 shows a stalls in the connecting state
and every few seconds cycles through an increasing number of bearers, never
settling.

The logs show:

journalctl -u ModemManager
May 17 11:53:20 325da06 ModemManager[1398]: [modem0/bearer17] connection
attempt #1 failed: QMI protocol error (14): 'CallFailed'
May 17 11:53:20 325da06 ModemManager[1398]: [modem0] state changed
(connecting -> registered)
May 17 11:53:20 325da06 ModemManager[1398]: [modem0/bearer17] connection #1
finished: duration 0s, tx: 0 bytes, rx :0 bytes
May 17 11:53:20 325da06 ModemManager[1398]: [modem0] simple connect
started...
May 17 11:53:20 325da06 ModemManager[1398]: [modem0] simple connect state
(4/8): wait to get fully enabled
May 17 11:53:20 325da06 ModemManager[1398]: [modem0] simple connect state
(5/8): register
May 17 11:53:20 325da06 ModemManager[1398]: [modem0] simple connect state
(6/8): bearer
May 17 11:53:20 325da06 ModemManager[1398]: [modem0] simple connect state
(7/8): connect
May 17 11:53:20 325da06 ModemManager[1398]: [modem0] state changed
(registered -> connecting)
May 17 11:53:20 325da06 ModemManager[1398]: [modem0/bearer18] couldn't
start network: QMI protocol error (14): 'CallFailed'
May 17 11:53:20 325da06 ModemManager[1398]: [modem0/bearer18] call end
reason (1005): gsm-wcdma-insufficient-resources
May 17 11:53:20 325da06 ModemManager[1398]: [modem0/bearer18] verbose call
end reason (6,26): [3gpp] insufficient-resources
May 17 11:53:21 325da06 ModemManager[1398]: [modem0/bearer18] couldn't
start network: QMI protocol error (14): 'CallFailed'
May 17 11:53:21 325da06 ModemManager[1398]: [modem0/bearer18] call end
reason (1005): gsm-wcdma-insufficient-resources
May 17 11:53:21 325da06 ModemManager[1398]: [modem0/bearer18] verbose call
end reason (6,26): [3gpp] insufficient-resources
May 17 11:53:21 325da06 ModemManager[1398]: [modem0/bearer18] connection
attempt #1 failed: QMI protocol error (14): 'CallFailed'

mmcli -m 0
SIM      |               dbus path: /org/freedesktop/ModemManager1/SIM/0
  -----------------------------------
Bearer   |               dbus path:
/org/freedesktop/ModemManager1/Bearer/802

mmcli -m 0 again, a few seconds later

SIM      |               dbus path: /org/freedesktop/ModemManager1/SIM/0
  -----------------------------------
Bearer   |               dbus path:
/org/freedesktop/ModemManager1/Bearer/1343

Again, an hour or so later:

SIM      |               dbus path: /org/freedesktop/ModemManager1/SIM/0
  -----------------------------------
Bearer   |               dbus path:
/org/freedesktop/ModemManager1/Bearer/16353

Has anyone seen this behavior before?  It's very odd considering that other
T-Mobile SIMs work fine on Balena, and this problematic one works fine on
non-ModemManager setups.
Thanks!
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