The bug happens as follows: start a fresh conversation with a new recipient in the Messages app, send a single emoji as the first message, and much of the interface will essentially go blank with the top menu disappearing.
The glitch effectively renders the Messages app unusable until it is force closed and reopened through the multitasking menu.
The bug has affected most iPhone, iPad, and likely iPod touch models since at least iOS 11.1.2. MacRumors is able to reproduce the issue on iOS 11.2, iOS 11.2.1, and the first iOS 11.2.5 beta released yesterday.
The issue is prevalent in both iMessage conversations with blue bubbles and SMS conversations with green bubbles.
While this bug is a minor one, it adds to a growing list of issues that have surfaced over the past several versions of iOS 11 and macOS High Sierra, including a major Mac vulnerability that provided easy access to the root superuser.
Beyond the root bug, Apple has also dealt with a HomeKit-related vulnerability, an iPhone camera autofocus issue, iOS autocorrect bugs, and iPhone X glitches in cold weather, among other problems, in recent weeks.
We've alerted Apple about this bug shortly prior to publishing this article and we'll provide an update if and when we learn about a fix.