Reason: High print density
High print density causes the label to get too hot and get stuck to the Printhead. Different labels require different heating temperatures. Set your print speed to "4 in/sec" and density to "2" and try print again. If the label is too light, increase the density by 1.
For Mac:
-> Select "Printer Features" in "Preview"
-> You can change the printing speed and the Darkness of your printing
(Larger number means higher Darkness)
For Win:
-> Go to "Control panel" -> "Devices and Printers"
(Right click on "This PC", choose "Properties", then click on "Control panel"-> "Devices and Printers")
-> Right click on "GFLP801" -> choose "Printer Preferences"
-> Go to "Set"
-> You can change the Darkness of your printing
(Larger number means higher Darkness)