We have purchased two pieces of the Arduino MKR NB1500. both of which sufffer from a modem lockup after 1-4hrs operation where a power down reset is required to get them working again.
They are both firmware rev 5.06 and ublox firmware release document https://www.u-blox.com/sites/default/files/SARA-R410M-02B-01_PCN_%28UBX-19024506%29.pdf for firmware 5.08 lists a lot fixes for modem lockups.
Will Telstra replace the MKR NB1500 boards we have with upgraded versions unser warranty? The firmware upgrade process is not very well documented and looks a little bleeding edge making it look fairly risky to upgrade the firmware ourselves.