When streaming FulGaz to an older-model Apple TV via AirPlay, you need to mirror the entire iPhone or iPad screen.
If you can only see see a video on the screen, your Apple TV is just playing the ride video at the speed it was filmed at, while you ride at your own speed in FulGaz. You need to either make sure you are mirroring your whole iPhone or iPad screen.
AirPlay also puts extra strain on your home WiFi network, especially if other family members are using it at the same time for YouTube, Netflix, online gaming, etc. Lagging over your network may cause the video and resistance to go out-of-sync if it cannot keep up.
If you have a 4th Generation Apple TV or newer (HD or 4K): Please install FulGaz directly onto your Apple TV via the App Store. This way you will not need to use your iPhone or iPad. This will give you much better performance and video quality and you can use your existing subscription.