You're using an iPhone, right?
The iPhone may heat up a bit while charging. To extend battery life, if the battery becomes overheated, the software may limit charging when the charge exceeds 80%. When the temperature drops, the iPhone charges again. You can also try moving your iPhone and charger to a cooler location.
If it is used by Apple mobile phone, it is recommended to choose a mobile power supply with Apple MFi certification and in line with the new national standard, such as green Apple mobile power supply.