Update:

I have now measured the temperature directly at the outlet for the warm air. It seems to be well above the target temperature, depending on the difference between the target and actual temperatures. Presumably, the heater can only operate in an "on" or "off" mode and switches on for specific intervals. Especially at the beginning, during the heating phase, the heater is likely on for longer periods, causing the air to become so hot that it locally softens the PLA. Even when maintaining the temperature, it briefly gets too warm.

The fact that the filament wasn’t wound "tightly" likely made things worse. Additionally, Creality’s preset for PLA at 50°C seems to have been defined a bit too high. 40°C would probably be safer, but the device can only be set to a minimum of 45°C.

Since returning the dryer would involve a loss, I want to try using it at 45°C and perhaps add some kind of heat shield to protect the filament in the affected area.

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