Well, I would have to say that, that one is hard to explain away, but unless someone was either the dumbest operator, or intentionally tried to mess up the spool, it would be very hard to get a quote knot in the middle of a spool.
Use critical thinking and you will realize that it is not possible to do that with a continuous run . Now they might of gotten slack in there spool and it might of kinked, but that is it. (maybe there not doing continuous runs I do not know)
Or maybe as I stated above they might have "not" held the end of the spool when they cut it, the same as many of us do, what this will cause is a back lash of the filament, and YES it could in that case have a "knot" in the middle of a 20 hour print. (although 20 hour print is not really relevant, I mean a 20 hour print could be 100 grams of filament or 300 grams of filament.) If the end of the filament snaps back it could easily get wrapped up enough to where it will run and continue to pull until it finally hits a stopping point. Don't think that the filament will stop as soon as it reaches the "knot", the knot will continue to move backwards until it reaches a point where the resistance is to strong especially if the spool is already loose from the snapping back of the end piece. And unless you where watching the spool the entire time, you really do not know when "all" the slack was out. Look at the blue spool above I'll bet you that, that is at least 200 grams of slack in that spool, and on a new spool that same amount of slack would be even more, because there is more surface area the larger the spool.
Finally, I personally, do not work for, with, around, or near Zortrax, So I have no reason to try and push responsibility off my back or there back. If you had really used critical thinking you would have realized that.
Also I will say that Filip said,:
"Richdon is right - almost every problem with spool is caused by inattentive loading/unloading filament."
"Many of the issues that customers are having with knots in the spool can be coming from unloading the spool and letting the end piece snap back."
Not once did he or I say that "ALL" problems are caused by user error.
Sorry if this comes off as a little rude or abusive, trust me it was not meant to be that way, I just get tired of people always thinking someone is trying to get over on them. The world is not out to get us all the time, maybe zortrax has some flaws here and there but tell me which company, or person doesn't.
PS please "TRY" to ignore my poor English Grammar above.