The SOA data in figure 11 on your data sheets references a single test pulse into the linear region, but in the case of switching this relates to the time in the linear region. For instance 30nsec transition ON to OFF allows you into the top right hand corner (as your graph implies). I think this is an industry wide confusion so would like to clarify this data as it relates to GaN FETs
Our SOA is not limited by hot spot formation / Spirito effect (we don’t have this problem) or second breakdown. During hard switching you follow the black square up to the worst case VDSmax + IDS condition.