Ruuvitag with external I2C sensor

I have attached a SI7055 temperature sensor to a Ruuvitag as I need 2x temperature sensors for an application. My simple test app is below . If I call readBmpTemp() I get a correct temperature. If I then call read7055Temp() - the first time I get an I2C arbitration error and then the second call works. If I switch back to readBmpTemp() the first reading is incorrect etc

Is there something I have setup wrong ?

var i2c;
var Ruuvitag;

function onInit() {
  Ruuvitag = require("Ruuvitag");
  Ruuvitag.setEnvOn(true);
  
  i2c = new I2C();
  i2c.setup({ scl : D28, sda: D29 });
}

function read7055Temp() {
  i2c.writeTo(0x40, [0xf3,0x40,0x40,0x40]);
  
  setTimeout(function() {
    var rawTemp = i2c.readFrom(0x40, 2);
    var val = (rawTemp[0] << 8) + rawTemp[1];
    var temp = (175.72*val) / 65536 - 46.85;
    console.log(temp);
  }, 10);
}

function readBmpTemp() {
  console.log(Ruuvitag.getEnvData());
}