This happens when the unstable power supply is used in the system unit, your intervention in the circuitry of the programmer, etc. , which leads to failure of firmware microcontroller programmer.
In this case, the programmer can be put into the bootloader mode.
Advice for TL866 programmer owners. If your programmer is not recognized by the system after the upgrade, you can force it into bootloader mode by supplying VCC (+3.3 V) through a resistor of 100-200 ohms to the specified point and performing a reset.
For this, the arrow indicated on the photo is supplied with a voltage of 3.3 V through a 100 ohm resistor.
This way we reset the microcontroller of the programmer and force it when connecting to USB, start the bootloader and when starting the software, make programming.
Or by connecting to USB or by closing the RESET pin on the ISP connector, which the manufacturer should inform TL866 users about. After activating the “loader mode” in the MiniPro TL866 programmer, you need to download the firmware again using the Mini Pro software.
Hope it helps.