Connected with iPad I can't start to ride

I connect to Zwift, start cycling, connect all the sensors, start a ride, enter in Richmond or NY for example and nothing happen. I remain on the edge watching the rest of riders.
This happens once or 2 every 3 ride. What should I have to fix ?
I use iPad to connect to Garmin Bike Speed 2 and Cadence 2 Sensor and bluetooth Decathlon ANT+/Bluetooth belt.
With Android smartphone everything is ok, except that the screen is too small.