Ever since the introduction of the ESS, maurauders have been used almost exclusively by the defenders to roflstomp ESS robbery attempts due to the fact that maurauders are so insanely more powerful than any other subcap thanks to bastions and can easy track anything in the ESS (cruiser and up), this allows them to wipe out entire filament fleets even solo in some cases due to their nearly invulnerable nature and the fact noones gonna filament a bunch of maurauders due to their cost. It often turns a bastion into a “i win” button in an ESS - this i believe has seriously hampered alot of small fleet/filament pvp fleets and reduced the total amount of destruction and fights occuring as most ESS attackers just run away when they see a maurauder as theres little to no chance of winning that fight.
The ESS disrupts all warp fields resulting in of all warping, microwarping and microjumping, the bastion module: “Through a series of electromagnetic polarity field shifts, the bastion module diverts energy from the ship’s propulsion and warp systems to lend additional power to its defensive and offensive capabilities.”, In lore it would make sense if the ESS disrupted the bastion.
Therefore my suggestion is that bastion modules simply do not work when within range of an ESS.