When does hazel normally execute rules?

Hi everybody!
I've been using hazel for quite a while now and have build a set of rules helping me to manage my nearly-paperless office.
I use a networked scanner to produce PDFs on a network drive. These files are then picked up by hazel, moved, renamed and sorted. All that works - in principle.
Sometimes, the files just sit in the hazel-monitored folders and nothing happens to them.
It looks like hazel has forgotten them. When I open up the hazel pref pane and check the rule for example, hazel starts executing them.
What am I doing wrong here?
Kind Regards,
Peter
I've been using hazel for quite a while now and have build a set of rules helping me to manage my nearly-paperless office.
I use a networked scanner to produce PDFs on a network drive. These files are then picked up by hazel, moved, renamed and sorted. All that works - in principle.
Sometimes, the files just sit in the hazel-monitored folders and nothing happens to them.
It looks like hazel has forgotten them. When I open up the hazel pref pane and check the rule for example, hazel starts executing them.
What am I doing wrong here?
Kind Regards,
Peter