The lintel at the garage door head is sagging.
The lintel is strong enough to carry the load from the masonry, but the I value (second moment of area) is insufficient.
It is very common to see the mortar joint/masonry near the central or at third points (车库门宽度的3分之一）of the garage door width is cracked when the actual deflection of the lintel is greater than the allowable (permissible) deflection.
As a result, section of masonry near both ends of the lintel will get 'push' out.
In your case, there is a substantial masonry section on the right hand side reveal (blue circled in the attached).
The masonry section on the left is smaller than the right hand side and is 'pushed' by the end of the deflected lintel. Hence, the stepped cracks on the top left corner occurs.
You need a deeper lintel section (deeper means a bigger H - see attached below) with the I value is greater than the existing lintel to support the masonry above.
Note-
1) ensure wall ties to the external leave is provided (see attached) - wall ties to be stainless steel or galvanised (to avoid future corrosion)
2) new steel lintel to be hot-dip galvanised (to avoid future corrosion). Normally, the thickness of the steel lintel is approx. 6mm (1/4 in). Once is corroded (without the galvanised protecting coat), it expands and this will cause the mortar joints to cracks. Then, rain/water penetration will cause lots of issues like dampness to the timber frame structures. In a long run, decayed timber will cause wood rotten/fungi etc.
Hope this helps.
