You had something similar happen when you were making some connector mods and the CS pin got left disconnected I think.
Along a similar line, when I first modified the prototype to go from ILI9341 to use the new ST7796, I forgot to cut an inner trace. That connected the display SPI MOSI pin to the display touch I2C SDA pin. Both the touch and display worked fine despite the combined signal looking like this, which is another head-scratcher.
Along a similar line, when I first modified the prototype to go from ILI9341 to use the new ST7796, I forgot to cut an inner trace. That connected the display SPI MOSI pin to the display touch I2C SDA pin. Both the touch and display worked fine despite the combined signal looking like this, which is another head-scratcher.