If your IX20 device revision is RevAN or newer, you cannot downgraded to a firmware version older than 23.6.1.105, otherwise the IX20 will not be able to establish a cellular connection.

 Starting in firmware version 23.12.1.56, the watchdog system inside the Digi router will automatically re-power the cellular modem inside the Digi router if the modem is not initialized for more than one hour, and reboot the entire Digi router if the modem is un-initialized for more than 2 hours.  Please read the release notes for information on disabling this option.