This seems to be a new problem after 0.13.8, never noticed it before.

Enemy fleet ships seem to be spawning on top of each other occasionally, and it really destroys my framerate. Going from 60 FPS to like 2 FPS, basically unplayable and I just have to immediately try and jump out of these systems rather than play through them.
Never happened before, now seems to happen quite frequently in Elite and Vanguard level systems. Admiral difficulty.