Old-time x86 sort-of has “states representable in registers but not main memory”, too.

Compilers used to use its 80-bit floating point registers for 64-bit float computations, but also might spill them to memory as 64-bit float numbers.

https://hal.science/hal-00128124v3/file/floating-point.pdf section 3 has some examples, including one where the assert can fail in:

  int main (void) {
    double x = 0x1p-1022, y = 0x1p100, z;
    do_nothing(&y);
    z = x / y;
    if (z != 0) {
      do_nothing(&z);
      assert(z != 0);
    }
  }

  void do nothing (double *x) { }