I've had that problem also with my Tomcat 8" PTO
chipper, same design as the Liberty. It's designed to run at 540 rpm which is 2200 rpm on my tach (Yanmar 2610 diesel 31HP, 26HP at PTO). But I run about 1800 because I just don't like running at rated speed. I ended up jamming the chute with fresh cedar trimmings, the green stuff really tends to jam the chute. One time I just took the chute off and it cleared itself on restart. I did about 5 hours of chipping over several months. Then I jammed it again on skinny cedar branches with lots of green. It jammed extremely tight. Took off chute and it was crammed in so tight had to dig it out. Long story short, I parked it after not being able to clear it. 6 months later I figured it would be mulch, so I fired it back up and after some heavy clutch popping it cleared.
Solution. Run at rated RPM. Stay away from freshly cut cedar with lots of green matter still on it.
I did 4 straight hours of chipping at 1800 rpm on a pile of 6-month old cedar clippings, no problems. Its the fresh cedar that jams it up. And even then, I think if I just ran it at rated RPM I would have been fine.