As Ray mentioned, the twine discs may be out of adjustment. Check their linkage, also they may be worn enough to not do their job consistently.
My experience has been almost all with NH balers. Relative has a JD 336 and at times it has been tempermental, though mostly it has given good service. During its last problem episode I drove the baler while he walked along and observed. I adjusted the throttle by ear which he said was faster than he usually ran it and he said it seemed to work better at the higher speed.
My observation is that square balers last longer and operate better if they are sheltered from the weather.