Thanks to Wort. It appears the BulletDeathByTargetProximity
game bug has returned with Cosmoteer 0.15.4c. This was found with the Flex missile defense turret but could also apply to energy mine, escalayer/fleet ballistic missile and the gravity mine. The crash happens regardless of whether the weapons hit or not and seems to involve when the target disappears. Hopefully, Walt will have it fixed once and for all soon.