That is clearly a flipped trianglulation between what the baked had during the baking as the lowpoly from what you actually have in your blender viewport. This is obvious from the x shaped normal map error patterns. Make sure you triangulate the mesh on export.
Looks like you triangulated your highpoly? Either way, the constricting edge on that flat plane doesn't follow the edge nicely. Try insetting the top plane once to make that edge uniform.
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