The engine's light rendering cap needs to be toggleable or increased.
Video of this bug/'feature' in action: https://www.youtube.com/watch?v=xSIkoyZuf1A
When the update came several years ago where Thrusters were given their own light sources, someone at keen got the idea to put a cap on how many lights can be seen on the screen at any given time before it stops rendering anymore. Particularly when there's a lot of thrusters on a ship or several ships in one area, this is often quite noticeable, especially as larger ships are more common now with recent game optimizations/advances in hardware over the years.
There's a few things that could be done to remedy this issue, the way I see it. One would be to give a set of options to the player, to enable/disable lighting limits or at the very least toggleable thruster illumination. Another would be to focus further optimizations on lighting itself to allow more lights to be rendered in a single scene, or re-evaluate what the game can handle currently, as even today it runs much smoother then back when these limits were first put in place.