Something seems to be modifying the backdrop object all the time. The values in the object are linked to something (I cannot find what) and there is some Xpresso script shown in the Object Manager, but I cannot see it anywhere in the scene, nor can I edit it!
Sorry, I'm stuck :-(
Most probably, the scene you sent is just broken. As a general rule, don't update the scene all the time using a script, because each update will restart the interactive renderer.