Found a bug recently when I swapped to using cannons in the damage calculation. When attacking shielded enemies the damage calculates just fine (4.4k damage for 4x cannons with 1.1k damage each). When the shields drop the damage drops significantly to around 1.1k. From the looks of things it only seems to be picking up on one shell hitting instead of all 4? Very occasionally it fails to register any of the shells hitting at all despite it being clear visually that they have.