If that same basic tongue design had a more substantial sandwich of materials, it would still be flying.
As the saying goes, "If you don't fold one every now and then, you're probably building too heavy". I would [after the benefit of seeing this failure] make the center ribs out of 5 ply aircraft grade wood and go double thick of what you show there.....I would also beef up the former in the area of the slot. The heavier center ribs could [should] have lightening holes judiciously placed safely away from the high stress area up front.
Then go thrash the plane for all it's worth with confidence.