I'm using RPi Zero W with 3.5" LCD driver ( here ). Everything works well except the UART. Linux console is disabled and UART is enabled. When video output is on HDMI port, I can send and receive bytes ( a loop back test program) on pin 8 & 10 ( GPIO 14 & 15) but when I switch to LCD output, it doesn't work.
OS version: Raspbian Buster, updated with the latest packages.
LCD connects to the board by SPI protocol.
I use LCD35-show script.