iPhone owners who have installed Apple’s new iOS 18 software update should be warned: There’s a Messages bug that can cause crashes and may even result in the loss of valuable data.

One of 9to5Mac’s readers spotted and reported the bug, which the site (having successfully reproduced it) then discussed in a news article Wednesday. The problem centres around an Apple Watch feature that lets users share their watch face over Messages (or Mail).

“The bug is triggered,” 9to5Mac writes, “when someone replies to a shared watch face in a thread on Messages in iOS 18… If this happens, Messages will repeatedly crash if the user tries to open the conversation in the app. Sending or responding to conversations from other chats directly in Messages is also not easily possible as the app may repeatedly crash.”

It’s a two-way issue, too. The bug affects both users.

As 9to5Mac explains, resolving the bug is extremely tricky. What you need to do is delete the conversation thread on both devices. It’s impossible, unfortunately, to delete only the thread, since neither user will be able to open it due to the bug. Even deleting the entire conversation will be difficult because Messages keeps crashing-and successfully completing this fix results in the loss of potentially years of conversation history and attachments. It may in fact be better to leave the bug in effect for now and hope that a future software fix enables it to be sorted without the loss of an entire Messages conversation.

And of course, it’s far better to avoid the bug in the first place and not reply to watch faces in a thread. And also install updates to iOS 18 in a timely fashion. The iOS 18.1 beta is still affected by it, but reportedly in fewer specific scenarios than iOS 18.0. And we assume a future updates will arrive before then to roll out a fix.