Hey neighbors! Chiming in for Tom here. The error that you are running into is actually by design. You can read more about this in our Community post about this feature update here, but the note in particular to call out from the article is as follows: " Note: Motion zones can not be extended to the full area of your Live View when creating these zones. This is because the area your camera covers is slightly larger than the area your motion sensors cover."
Please note that you may not be able to cover your full live view, but the boxes you are drawing is the area that your motion sensor on your battery device can cover. You will not run into this when drawing zones for hardwired/powered devices such as the Ring Pro, as the motion sensing technology in it if from Advanced Pixel Detection and not PIR Motion Sensors like the battery devices. Hope this helps clear this up for you!