@JBaldwin Thanks for the insights, always nice to read how others solve similar problems.
Particle spawning should be completely independent of the material. Did you check in another viewmode if they really aren’t there? My initial guess would be that the way you calculate your mask is not updated when the particles move, leaving the initially masked particles masked forever and the other never to be masked. Try plugging the mask into the emissive slot or enlarging them to usually be partially masked to more easily debug them.
PS. Did you post another question before? I got an email from the forum telling me so, but there was nothing in thread…