Some Lenses aren't supported on older devices, due to technical limitations. For example, video capture with face shift Lenses aren't supported on older Android devices. If Lenses aren't working properly on your device, you can try using different Lenses or using Snapchat on a different device.
Lenses are supported on Apple devices with iOS 12, or newer, and most Android devices with Android 4.4 (KitKat), or newer.