A bug in Android 8.1 Oreo that causes the touch screen to detect touches that never happened in certain scenarios involving multitouch has officially been pinpointed in the Android code review, which means that a fix will almost certainly come with the June 2018 Android Security Bulletin. Major changes and fixes need to be put into the codebase at least one month before patch releases in order to allow time for testing, which means that the bugfix being found in the middle of April excludes it from appearing in May's patch. The fix is ready to implement at this stage, which means that Google is likely already working on getting it patched into the upstream AOSP code, and from there, it will spend May in testing. Since the bug in question is a major one, the company may expedite testing and rollout of the fix, but there is no guarantee of that.
The bug being referenced pertains to multitouch on some Android 8.1 devices, most notably the Pixel 2 and Pixel 2 XL. When touching two or more points repeatedly, a bug pops up when a touch point is glanced over that was already touched, or when one point passes over somewhere another has recently been. The bug causes random touch events to be sent as part of the multitouch set. According to the fix posted in the Android code review, this bug is due to a resampling error that ends up miscalculating touch points when they're calculated relative to one another. The fix is to have resampling done on an individual touch point basis, then relay the data for processing into multitouch, rather than processing multitouch synchronously. In testing thus far, the fix seems to be working.
Major glitches in new versions of Android can crop up quite easily due to the sheer amount of code in each release, along with the wide number of devices that have to be supported by that code. Usually, such bugs are dealt with in short order by Google's Android team. This particular issue seems to only affect a small subset of devices, and it looks like the team already has the fix built into the Android code and ready to roll out to users, as stated above.