5. Get this, Tera Term can successfully connect to Arduino UNO on COM6 but PrintCapture cannot. Why?
the source code for the Atmel ATmega16U2 USB controller might be a good start
is GitHub://Arduino/hardware/arduino/avr/cores/arduino/USBAPI.h a good start?
Your not trying to connect to the Arduino while Tera Term or the Serial Monitor app are connected, are you?Perhaps asking the PrintCapture people would be more appropriate.
The firmware for it is here:https://github.com/arduino/Arduino/tree/1.8.2/hardware/arduino/avr/firmwares/atmegaxxu2