Unicode::snprintf() Problem

I'm working with the STM32F769I-DISCO board and I'm having issues with the snprintf() Unicode function.

When I try to print a string to the screen only a few characters register, the rest show up as unknown characters.

For example, when I try to print "hello [x value]" to the screen, it prints "?ell? ?" instead.

Any advice?

Thanks

void mainScreenView::set_test_X()
{
 test testx;
 int x = testx.get_testX();
 Unicode::snprintf(textArea1_1Buffer, TEXTAREA1_1_SIZE, "hello %i", x);
 textArea1_1.setWildcard(textArea1_1Buffer);
 textArea1_1.invalidate();
}