This is mainly due to the current collision algorithm which is decent, but not ideal as you can see. It can miss higher speed object.
To improve things, try increasing the collision radius of the particles slightly. This will fill in gaps between them. Also, in Project Settings -> VICO Dynamics, try increasing the substep count a bit and the constraint iteration count a bit. Be aware that performance will be affected and going too high can result in strange behaviour.
Testing the soft-body stuff was too much fun, I found myself just messing around with them for hours 