It seems like there is a weak bond in the singlefacer and/or doublefacer. This could be due to the medium having a significantly higher floatcurl (water drop) than normally run at the plant. Floatcurl refers to the amount of water retained in the corrugated medium after passing through a conditioning unit. When the floatcurl is high, it can cause the adhesive to become diluted and reduce its effectiveness in bonding the medium.

To fix this issue, it's recommended that you reduce the adhesive viscosity at the single facer. This can be done by adjusting the adhesive formulation or changing the application rate. Additionally, you may want to consider increasing the preheating temperature of the medium to improve its ability to bond with the adhesive.

It's important to note that weak bonding can lead to various issues such as warping, delamination, and reduced box strength. Therefore, it's crucial to address this problem as soon as possible to prevent any further complications. Let me know if you need any further assistance.