Looking this thread over, I don't see mention of which side of the sheet is receiving the score.
So, at the risk of saying what is obvious to some of us who come from a letterpress background: make sure that your score, if a single score, is striking the outside of the fold rather than the inside, to make a set of hinges rather than a smash.
Without having a letter press is there other ways to create the channel score effect?
Yes, you can come up with a reasonable channel score by running 2 scores in close register separated by about 1/32"-1/16" (1mm) or so (depending on thickness of paper). This will give you a double hinge score, which may solve your problem.
Another trick that I have used on
very short runs is to run a
very lightly dampened cloth over where the score will hit. (Obviously, check to see that it works before you waste a job.
) Often, the increased moisture in the paper will be all you need.
Also, consider using an uncoated, smooth finish sheet.
And of course... avoid a crisp fold.
As you have probably guessed, your problem is made worse than it could be because you are running digitally. Adhesion of toner to sheets is usually much more fragile than ink staining.
This actually can be an opportunity for you to upsell the job from digital to presswork.
Never forget that option. You're in business to make money from what you produce.