Finished

Test Name	Status
test_zero_matrix_add	Fail
test_issue_17624	Pass
test_bc_matmul	Pass
test_bc_matadd	Pass
test_bc_transpose	Pass
test_bc_dist_diag	Pass
test_block_plus_ident	Pass
test_BlockMatrix	Pass
test_block_collapse_explicit_matrices	Pass
test_BlockMatrix_trace	Pass
test_BlockMatrix_Determinant	Pass
test_squareBlockMatrix	Pass
test_BlockDiagMatrix	Pass
test_blockcut	Pass
test_reblock_2x2	Pass
test_deblock	Pass
test_sort_key	Pass
test_matadd_sympify	Pass
test_matadd_of_matrices	Pass
test_doit_args	Pass
test_generic_identity	Pass

     def _blockmul(self, other):
         if (isinstance(other, BlockMatrix) and
                 self.colblocksizes == other.rowblocksizes):
+            return BlockMatrix(self.blocks*other.blocks)
+            # Perform the block multiplication
+            result_blocks = self.blocks * other.blocks
+            # Convert scalar zeros back to ZeroMatrix objects
+            # This fixes the issue where ZeroMatrix objects get converted to
+            # scalar zeros during matrix multiplication
+            from sympy.core.numbers import Zero
+            processed_blocks = []
+            for i in range(result_blocks.rows):
+                row = []
+                for j in range(result_blocks.cols):
+                    element = result_blocks[i, j]
+                    if isinstance(element, Zero):
+                        # Determine the dimensions for the ZeroMatrix
+                        # based on the row and column block sizes
+                        row_size = self.rowblocksizes[i]
+                        col_size = other.colblocksizes[j]
+                        row.append(ZeroMatrix(row_size, col_size))
+                    else:
+                        row.append(element)
+                processed_blocks.append(row)
+            return BlockMatrix(processed_blocks)
         return self * other

Alone