If you enable a cameraA component which creates an image of a particular viewpoint in your scene. The output is either drawn to the screen or captured as a texture. More info
See in Glossary at runtime, mipmap streaming needs time to stream the mipmap levels into memory.
You can use texture preloading to prevent this. Do the following:
Use StreamingController.CancelPreloading to cancel preloading.
You can use the following APIs after you enable preloading:
If these APIs return values that indicate Unity has finished preloading, you might need to wait a few frames before you enable the camera to make sure preloading has finished.