I have had a look at the IridiumSBD library, and there are multiple points which could trigger the watch dog timer (WDT). These are mainly a sort of wait for response loop.
Since you are using the SerialUSB for the debug output, it is likely that the reset is appearing as a freeze. This is due to the SerialUSB connection being reset when the board is reset (by the WDT).
When the tracker starts up it should show the cause of the most recent reset. However, if you are using SerialUSB for the output, this is usually missed as the connection is closed when the board is reset.
I would normally recommend using another UART for debug. However, this might be difficult as the Roadblock device is using the only externally available UART one the SodaqOne. (It is possible to add another UART mapping if required, but this will take some modification of the board description files.)
If you can find a terminal emulator which will automatically attempt to reopen a closed connection (if such exists), you should be able to catch the cause of the reset and confirm that it is the WDT.
I am going to create a WDT compliant version of the Roadblock library. However, at least initially, I won't be able to test it directly myself. I may need your help in testing out the changes.
Is this the library you are using: https://github.com/mikalhart/IridiumSBD