Quite a few Pixel 3 XL owners along with YouTubers have discovered that a software glitch has resulted in their phones suddenly sporting an extra notch on the side of the phone. This only affects the Pixel 3 XL as the regular Pixel 3 does not have the notch to begin with, so it looks like it might have to do with the software that Google uses to adjust the look of the corners on the phone.
Other possible reasons for the bug could be in the developer options used to simulate a notch that are somehow accidentally triggered. Either way the good news is that a reboot of the phone seems to make the problem go away, at least for a while until whatever triggered it makes it pop up again.
Thankfully Google is aware of the issue and have told the folks at XDA that a fix for the problem is coming soon. In the meantime like we said, if you run into this issue then performing a quick reboot of your phone should solve it.
https://twitter.com/UrAvgConsumer/status/1055215243637460992