Your Pixel 3 XL could have had TWO notches
The Pixel 3 XL was rumored to have an extra deep notch several weeks prior to its launch in September 2018. It did indeed sport this notch on its debut, which turned out to be so big in order to house the phone's dual selfie cameras and top-edge speaker. Since Google had embraced the notch in its own hardware, it was up to the company to support the resultant display cut-outs in software (i.e. Android 9.0) so that it didn't interfere with apps and the user experience.
In some respects, it appears that these attempts have failed so far. At least one reviewer has noted that the notch impinges on the visibility of full-screen YouTube videos while using the Pixel 3 XL. When in zoomed-out modes, the notch may 'shove' the video window off to one side. However, it appears that this is not the only problem the phone's software has with the notch.
A Redditor has recently posted an image in which a Pixel 3 XL appears to have 2 notches: one where it actually should be, and a software-recreated one on the right edge of the screen. This in fact contradicts Google's own rules about notch adaptations for OEMs and apps: they state that there are to be no notches along the longer edge of a device. Nevertheless, the Redditor asserts that the second notch persisted until the phone was rebooted.
Therefore, it appears that a Pixel 3 XL could have come with more than one notch: one along each shorter edge, for example. This may have given more screen real estate, but also invited far too many software issues. As for the alleged secondary notch anomaly, it could have been an error resulting from transitioning out of an app in landscape, or some similar bug. Then again, that explanation does the apparent stability of Pie while maintaining notch compatibility no favors. Whatever the issue really is, Google has claimed that they are now working to fix it.