[Mark Hafley]

I had the exact same problem. I think I cracked the case:

The ‘glowing line’ uses a blurred circle as a particle source. This is the SHAPE, not the PARTICLE EMITTER. I had duplicated the glowing line and used it in 2 places in my animation. Both of my emitters referenced the same shape as the particle source. That is the problem. Ensure that each emitter has it’s own ‘blurred circle’ shape, and that each ‘blurred circle’ shape is in the same group as the emitter.

The solution:
Duplicate the ‘blurred circle’ and move it to the same group as the particle emitter. Then, drag the ‘blurred circle’ shape to the ‘particle source’ well on the emitter tab. This should fix the glowing line immediately. No need to save, close, re-open, etc.

If you only have one emitter, duplicate the ‘blurred circle’ shape (again, this is the shape, not the particle), drag it to the ‘particle source’ well and delete the original ‘blurred circle’ shape.

This turned a very unreliable graphic into a rock-solid one. Hope it helps some of you that might have the same problem.