For over a year now we've had reports of the minefields in fleet missions being implausibly hard to destroy. I've done some tests and never quite worked out what was going on...until doing the simple tests just now. We have something seriously wrong with the hitboxes on the vanilla mines (as well as modded clones, such as those in Elemental Shift), and the most likely candidate is that the engine is ignoring the bitmask when working out where something can be hit. Assuming this is correct the bug has the effect of making it almost impossible to shoot down a mine (or other projectile with an animated sprite), making the fleet escort missions drastically harder than intended.
To replicate: Try shooting at an armed enemy CRM100 or sapiens radiation mine. Try a few different angles: you'll find that most shots will pass harmlessly through the sprite, but shots hitting exactly the right spot will damage or destroy the mine consistently. On angles where the shot doesn't connect it will never connect; this means the problem is not in interaction. A single TeV9 blast is also capable of taking out a (modded, Elemental Shift) CRM100 in a single hit, suggesting that raw missile HP is not the reason for the reports of invincible minefields.
I think we've got about a 1x1 pixel hitbox going on under all this and because the player can't see it, the mine sprites wobble (by design, since they're animated) and vanilla autoDefenseDevices aren't that accurate on moving or turning ships...this makes mines almost impossible to effectively shoot down with normal projectile weapons. This does give me some ideas for a mine-clearing item for fleet use, but should be fixed in the core game.
Screenshots show tests of this phenomena on the stock Sapiens Radiation mines around a sapiens base, and on a CRM100 clone used by the Rogue Fleet station minelayers in Elemental Shift. In both cases the projectiles fired by my ship are passing through the sprites of the mines without interacting them, even when shot at repeatedly.