This happens to all particle systems. I tried:
Changing the rendering mode to camera, setting culling mask to UI, particle system layer set to UI
Adding a canvas child, and attaching a particle system to this child
Tinkered with the camera's FoV and projection.
What happened was that the particle system worked in some areas of the UI, and was quite unstable, i.e. could disappear and appear again. I resolved it by adding a sorting group and setting order in layer to 1.
So my question is, why did it work so unstable? In all tutorials I saw it either worked 100% or not at all. What could cause its instability? In the first image, the ps is visible, in the other two not, after I moved it (left and right). So what causes this issue?



Sprites are sorted by their center point, so if the center point of a sprite in the corner happens to be closer to the camera than the center point of the card backing, it will sort in front. You might want to use a Canvas for this - then you can control the layering through canvas hierarchy order, without stacking up z offsets.It might be similar to your problem \$\endgroup\$