I moved the snowflake emitter plane to an unused layer, added a new one and added the same particle system as the old one. The new plane works like a charm. I have no idea why, though.
I’m doing a tutorial here: https://www.youtube.com/watch?v=aFnbcl6Kfj4&t=55s On the snowflake emitter I used a group. Also, the material is more complicated. I still can 't figure out why my snowball emitter object snowballs appear in cycles render but the snowflakes from the snowflake emitter don’t. Can someone tell me what I am doing wrong?
Blend file: http://pasteall.org/blend/index.php?id=44804