Image 1 - a blur effect rendering correctly (the color of the glow stays pink).
Image 2 - the same blur effect applied to different illustration within the same file but on different layer. It does not render correctly, as You can see (white instead of pink)
Image 3 - both these elements copied to third layer within the same file and they both render correctly.
Image 4 - the same element as in Image 3, copied to the layer where it doesn't render correctly
QUESTION: what's going on?
Your problem could simply be the background color.
In CMYK, blurring (and other smooth gradients) doesn't always work if the two colors don't share at least one ink. Your lines are mostly magenta, so the background needs to contain magenta for Illustrator to be able to make a smooth transition.
In the example below, the left side of the line has a much more pleasing transition, because the background is a rich black which contains a large amount of magenta. The right side is just plain black so Illustrator struggles to make a nice transition.
If you don't really care which CMYK numbers you are working with, you could maybe benefit from working in RGB mode. Everything involving blending colors is much smoother. You could flatten your artwork and convert to the appropriate CMYK profile at the end.
BTW: Make sure that "Appearance of Black" is set to display and output all blacks "Accurately".
