Particle point render type not hardware rending correct size on some machines
When render type is set to Points or Multipoint and Line Smoothing is turned on, the point size is limited by the graphics card on your system. Please see the hardware specifications of for your graphics card.
worldVelocity and aim direction
You cannot use the worldVelocity attribute as an aim direction for instances.
Keep the particle transform as the identity and use the velocity attribute.
Particle system can have inconsistent results between disk cache and non disk cache when using rand() in expression
Point and multipoint types w/line smoothing render differently
A particle rendered “as transparent” shows up differently if line smoothing is on vs. when it is off, even with identical opacity values.
Add an opacity attribute to the particle shape. (This doesn't hurt if you are turning geometry masking on, since all particles are transparent anyway.) Tune the opacity value to get the look you want.
Shader glow on particles may flicker
Positions of emitted particles incorrect when parent particle hidden
If Particle A is emitting Particle B and Particle A has any animation on it, either with fields or emission, the positions of the emitted Particle B particles will not be correct if Particle A is hidden.
Keep Particle A visible, but give it an opacity attribute with a value of 0.
Expression on “active” attribute may cause evaluation failure
Expression on “active” attribute may cause evaluation failure in rigid solver
Key the active attribute using the menu items provided for that purpose.