If you are having trouble uploading to Nextion from Nextion Editor (via USB serial), while using external power supply adapter to power the Nextion and a separate USB serial adapter to talk to the Nextion, you probably need to connect together the grounds from both the power supply adapter and serial adapter.
Power Adapter Nextion
USB Serial Nextion
GND GND (Power Adapter -)
about 2 years ago
Its one of the Iteadstudio problems! People dont have much information about the screen and they dont give the right support to their clients. !!!!!