NH 640 autowrap issue

I have a NH640 roller which has worked great for years.  Last fall, I noticed that it would not trip on some rolls.  I noticed it again this fall.  Spring rolling worked fine.  I am thinking the issue is related to the hay being less rigid (better hay, not as many stems) in the fall than in the spring.  I have to manually trip each roll.  String cuts ok when it completes the cycle.

 

I did try to activate the wrapping when the roll was full by pulling on the arm that activates it.  It would trip but the linkage would get stuck(probably because I had to yank it pretty hard).

 

Any suggestions?

NH 640 autowrap issue