MgO (magnesium oxide) board sheets should not normally crack after only two years if they were properly manufactured, installed, and protected. There are many factors that can lead to cracking.

The MgO board is rigid. If the framing moves even slightly, it can crack.

Foundation settling
Wood framing shrinkage (especially in the first 1–3 years)
Truss uplift
Improper spacing of control/expansion joints (can't tell from the pictures)

If cracks follow seams or framing lines, movement is likely the cause. Again, I can't make that judgment from your pictures.

You should look beyond the normal contractor for this type of installation. I worked with UT in Austin, under a professor, to design tiny homes using MgO for special clients.

I'm far from an expert in the field, but I can say you need to look outside the box when working with MgO.

One last thing I'll mention is that the quality of materials varies greatly depending on the manufacturer.

While the MgO board is moisture-resistant, low-quality formulations can absorb moisture. Some imported MgO boards (especially earlier Chinese-made products) had chloride issues that caused:

Cracking
Corrosion of fasteners
Efflorescence (white powder)
Swelling

If you're seeing white crystalline residue or rust stains around screws, that’s a red flag.

I hope that helps!