diff --git a/network_process/src/post_topo/filter_chains.cpp b/network_process/src/post_topo/filter_chains.cpp
index 44028a0..81c86ab 100644
--- a/network_process/src/post_topo/filter_chains.cpp
+++ b/network_process/src/post_topo/filter_chains.cpp
@@ -1,5 +1,6 @@
 #include <post_topo.hpp>
 #include "container/wrapper/relation_graph.hpp"
+#include "fwd_types.hpp"
 
 void filter_chains(const stl_vector_mp<polygon_face_t>&                  faces,
                    const stl_vector_mp<stl_vector_mp<uint32_t>>&         patches,
@@ -24,11 +25,17 @@ void filter_chains(const stl_vector_mp<polygon_face_t>&                  faces,
                 return tri.chain_index == triangle.chain_index;
             });
             if (iter == chain_triangles.end()) {
-                auto& mapped_tri       = chain_triangles.emplace_back();
-                mapped_tri.chain_index = tri.chain_index;
-                mapped_tri.v1          = vertex_old_index_to_unique_index.at(tri.v1);
-                mapped_tri.v2          = vertex_old_index_to_unique_index.at(tri.v2);
-                mapped_tri.v3          = vertex_old_index_to_unique_index.at(tri.v3);
+                auto v1_iter = vertex_old_index_to_unique_index.find(tri.v1);
+                auto v2_iter = vertex_old_index_to_unique_index.find(tri.v2);
+                auto v3_iter = vertex_old_index_to_unique_index.find(tri.v3);
+                if (v1_iter != vertex_old_index_to_unique_index.end() && v2_iter != vertex_old_index_to_unique_index.end()
+                    && v3_iter != vertex_old_index_to_unique_index.end()) {
+                    chain_triangle_t mapped_tri{};
+                    mapped_tri.v1 = v1_iter->second;
+                    mapped_tri.v2 = v2_iter->second;
+                    mapped_tri.v3 = v3_iter->second;
+                    chain_triangles.emplace_back(mapped_tri);
+                }
             } else {
                 // mark chain on this subface has double sides by all invalid vertex index
                 iter->v1 = invalid_index;
diff --git a/network_process/src/post_topo/patch_propagation.cpp b/network_process/src/post_topo/patch_propagation.cpp
index 6d6408b..b43af3d 100644
--- a/network_process/src/post_topo/patch_propagation.cpp
+++ b/network_process/src/post_topo/patch_propagation.cpp
@@ -118,13 +118,14 @@ dynamic_bitset_mp<> filter_cells_by_boolean(const baked_blobtree_t&
             // do bool operation, util meet next primitive node.
             assert(iter->is_operation_node());
 
+            // HINT: other_cell_signs here should always be left nodes
             const auto& other_cell_sign = stacked_nodes.top().cell_signs;
             switch (iter->get_operation()) {
                 case internal::eNodeOperation::unionOp:        temp_info.cell_signs |= other_cell_sign; break;
                 case internal::eNodeOperation::intersectionOp: temp_info.cell_signs &= other_cell_sign; break;
                 case internal::eNodeOperation::differenceOp:
                     // stacked nodes are always left childs
-                    temp_info.cell_signs &= ~other_cell_sign;
+                    temp_info.cell_signs = other_cell_sign & ~temp_info.cell_signs;
                     break;
                 default: throw std::runtime_error("ERROR: baked blobtree with unknown type operation node"); break;
             }