A little more digging here led me to a solution - and my Sat Nav GPS in now working correctly.
This page helped out as I didn't know the unit ran Windows CE in the background.
2014 i30 GD Premium - Sat Nav and head unit issueThanks
@rajiemoore After entering test mode and getting to the navigation software directory ( a bit tricky to drive CE with touch ! ) double clicking on the program labelled MTX1200-GD - came up with an error message - Sorry I didn't screen shot it but it was something like :
There was an error with your settings - select yes to reset to default - it mentioned something about losing your driving history and such but I figured it was dead anyway so worth a shot.
Selecting Yes allowed the GPS software to actually load - at this point it defaulted to an area in Sydney somewhere I think and a big Acquiring Satellite message - this didn't actually do anything else at that time and none of the radio buttons did anything , while mucking around I accidentally hit the start button and suspend ( which just made the display go black and I couldn't get out of it ).
I left it for a couple of hours and when I started the car again it just restarted as usual and displayed the Hyundai splash screen and then the sat nav worked again after hitting the ok button - the Fault in Main thread error hasn't reappeared so far. The clock time reset after a couple of minutes driving to the right time as I guess it syncs to the GPS as well.
Lost a couple of customization settings which didn't take to long to correct - the maps and software version seems to be the same so this seems to be a good option to try if your stuck with the same message - might as well give it a go if your stuck and contemplating buying a new unit.
Steps from the link above
To do this you can:
1. Hold the Settings Cog button to access the firmware/bluetooth version info
2. Press and hold the centre of the screen for about 20 seconds to enter Test Mode (Dealer)
3. Enter the code 159357 to access Windows CE
Once inside Windows CE you can navigate using the Touchscreen to the Navigation App which should be under My Device/Storage Card4/NNG there is a program labelled MTX1200-GD called IGo Primo Motrex 1.1. Double Click on this to start the Navigation,
And hopefully it will present you with the message to reset the settings - clearly this is a bug which stops the GPS software from loading and causes the lockup.