It may be that the output of the mobile power supply does not match the input of the phone.
When the mobile power supply charges the mobile phone, it must first sense the current of the mobile phone before it will charge normally. When the output current of the mobile power supply is relatively small, the mobile phone may automatically disconnect and charge in order to protect the battery.
At this time, the mobile power supply can not sense the current of the phone, and the mobile power supply will judge that the phone is full, and it will automatically disconnect and charge.