Hi. I think it happens when Xparticles runs out of RAM.
How much Ram do you have on your system?
I’ve got 64gb on mine. The partitions I did for the tut render had 1 million particles in total, although at this amount the machine grinds to a halt. Maybe try caching an Xparticles sim and have a look at your system performance to see how much RAM it’s using, and then try and work out what your max particles per scene is for your setup.
B