Small grain facets in the middle of the snowpack just under a faint crust and on top of a more stout crust seem to be the most likely trouble layer. With a more connected surface slab I would expect to see avalanches breaking out on this layer.
Depth hoar low in the snowpack is also a possible failure or step-down layer. In tests in two pits in similar areas one pit produced propagation on this layer (ECTP22) and the other (ECTX).
Surface snow was largely unconnected and susceptible to sloughing.