PARTICLES ARE IGNORING MASKING OPTIONS WHEN USING A MASK

I can't reproduce this problem. Are you sure you actually created a gameobject with the "SpriteMask" component and picked a proper sprite as mask? Tried to lower the alpha cutoff?

I simply used this sprite as mask. This is the particle system without mask.

Here is how it looks like with visible inside and outside.

I also had this bug when trying particles inside mask. Particles work fine in scene mode, but when I try in play mode it does not render. I found that this is caused by Z position. If Z is lower than mask, particles are not rendered. This behaviour exists only when "Visible inside mask" option is set. Sorting layers do not matter and turn useless at this point. Its a pity, since now I have to overhaul a massive amount of different spawner prefabs.

In case someone else ends up there with a similar issue, especially when your particle system is on a dedicated layer: The mask may simply not work if your "post processing layer" is after the script which blits the rendering to render your particle system on a different layer. The post processing layer script has to be before the other script.