ModemManager - connecting multiple modems simultaneously always fail

[Lucas Pelegrino]

Hey guys. I’m trying to connect 3+ modems on my PI, all of these modems are
working if I connect them individually, but once I connect all of them
together I get at least one that can’t get a connection.

Something always happens on the third modem that makes it stay in a unknown
state:

  -------------------------
  General |           path: /org/freedesktop/ModemManager1/Modem/3
  -------------------------
  System  |         device:
/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.1/1-1.1.2/1-1.1.2.4/1-1.1.2.4.6
          |        drivers: qmi_wwan, option
          |         plugin: generic
          |   primary port: cdc-wdm2
          |          ports: cdc-wdm2 (qmi), ttyUSB7 (at), ttyUSB8
(at), wwan2 (net)
  -------------------------
  Status  | signal quality: 0% (cached)
  -------------------------
  Modes   |      supported: allowed: any; preferred: none
          |        current: allowed: any; preferred: none

This modem works when I connect it by itself. I also tested different
permutations and it seems it’s always the third modem that can’t get a
connection, independently of which one I put on first. This is the full log
with debug on: https://pastebin.com/L3QWBppt

Any ideas?
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