Several of us at AP, myself included, have noticed a concerning stability issue on Google Pixel devices in recent weeks that causes the whole system UI to become unresponsive. According to the many replies to Artem's tweet on the subject (below), users of phones from other OEMs also complain about the issue, so it might be a more widespread Android bug rather than one limited to Google-made devices.

It's hard to show you the problem in a screen recording since it occurs at random — when a particular app freezes up, the entire system UI can become locked in an unresponsive state as well. You can't use the home button to leave the app and you mostly can't pull down the notification shade to escape that way either. At this point, locking and unlocking the phone seems to be the best course of action, although it's been suggested that swiping down on the fingerprint scanner can still bring down the notification shade on phones that support the gesture (Pixel 2 and 3). This can be frustrating as a one-off, but it's happening multiple times a day for some users.

Another thing that really bothers me on the Pixel 4 XL - when an app freezes up, it oftentimes locks up the whole UI. Notifications, home gesture - everything becomes unresponsive. Sometimes the UI unfreezes when the app does, sometimes the app remains frozen. Anyone else? — Artem Russakovskii (@ArtemR) April 17, 2020

While the majority of cases we're aware of are on Pixels with Google's built-in launcher, there are reports of the same problem from owners of OnePlus and Xiaomi phones, too, with Nova Launcher and Action Launcher not immune from experiencing it either. The apps that have been noted to cause the behavior are mostly unsurprising. Amazon, Twitter, YouTube, YouTube Music, and the Play Store have all been implicated.

Most of the phones said to exhibit the issue are running Android 10, but we also know of an affected Pixel 3 on the Android 11 developer preview. All of this is reminiscent of the frustrating memory management issues that afflicted the Pixel 3 and 3 XL, and if left unchecked, it could be even more problematic for Google given that numerous different models and OS versions are susceptible. We've reached out to Google to make sure they're aware and we'll update this post if they come back with information about a fix.