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Are you using a silicone sock on your hot-end. This is required if you have printed your cooling duct in PLA (even for some PETG, depending on the size of your hot-end and positioning of the cooling ducts). Have you tightened the screws that hold the cooling ducts well to the base, it is possible from the vibration of the hot-end moving around (especially with lots of tiny movements) to have the cooling duct slip it the screws are not tight enough. If that is not it, then it is likely the cooling ducts have warped from the heat of the hot-end. I only run the bed temp to 60c and the hot-end to 230c (with PLA or PETG printed cooling ducts). If you are using higher temps, this could be the cause. I have never tested the Hero Me with ABS (that usually needs 90-100c bed and 250c nozzle temps), in those scenarios, the Hero Me ducts should be printed in ABS.
Best position of the cooling duct is when the nozzle is touching the build plate, the bottom of the cooling duct should be between .1mm and .2mm above the build plate (varies due to the type and height of the nozzle you are using). I set mine to .12mm off the build plate.