Paper recognition function does not work reliably in label mode. How do I solve this issue?

You can use the automatic calibration function to solve this issue.
1) Turn off the printer in the label mode.
2) Turn on the power while depressing the Feed button.
3) Check the printing, and press the power button one more time to use the automatic calibration function.
Mode selection
a. Automatic calibration function: Press the Power button
b. Self test: Press the Feed button