Timeout on I2C Write BUSY - not all the time - SSD1306

Ok, well this is odd. I've got a SSD1306 (the one actually pictured in http://www.espruino.com/SSD1306) connected to a Pico running 2v07 and the exact JS code in the example, and it works great!

function start(){
 // write some text
 g.drawString("Hello World!",2,2);
 // write to the screen
 g.flip();
}

// I2C
I2C1.setup({scl:B6,sda:B7});
var g = require("SSD1306").connect(I2C1, start);

So I wonder what the difference is with your setup?

Worth noting that Software I2C is able to use the internal pullup resistors, but for some reason hardware I2C isn't - so if the I2C device doesn't have internal pullups then software will work but hardware won't.