What is the particle system comprised of? I would think that if it’s a two-sided material and uses scaled / modified bounds, then non-uniform would be necessary…but not constrained to the X axis (there’s two in Screen Align settings, one constrained and one not, so try the one that is not). Leave it there, then try changing other settings in tandem and independently. I know it’s trial and error, but it could reveal something that results in a better understanding of the actual problem. A few other questions:
Does the particle system have a sprite sheet (not one sprite image, but a series for animating…though I figured you know what that is)?
Is there an Initial Location module in use? or is it located based on what’s in the Required / Spawn modules?
Is it using a vector field?
Are the bounds completely encapsulating the system? As far as I know, when bounds are crossed by particles, it could result in viewing / rendering issues.