The watchOS 11.3 software update, which Apple rolled out Monday, includes at least one important security patch. But the release also brought an unintended side effect: it caused software updates to break on older Apple Watch models.

The bug was spotted by an X user and flagged by a MacRumors reader. Paradoxically it only affects devices that cannot install the newest update. Since it came out, owners of Apple Watch models that do not support watchOS 11 (anything earlier than the Series 6 and 2nd-gen SE) have found they cannot install the newest version of watchOS 10 (10.6.1).

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If they’re already running watchOS 10.6.1, which came out on August 19, 2024, your watch will be fine; it won’t get deleted from the device. But anyone trying to install it for the first time will be unable to do so. WatchOS 10.6.1 is the most recent version of watchOS 10.

As the original post explains, CV refers to the compatibility version and Apple mistakenly changed the over-the-air update requirements for pre-watchOS 11 devices. This also means that some Apple Watches running earlier versions of watchOS 10 have lost the ability to pair with an iPhone. Apple is likely to fix the problems as a matter of urgency but hasn’t yet commented.

It’s troubling that a bug this consistent was missed in the testing phase, but perhaps not entirely surprising; it would make sense, after all, to test on the watch models that will be running the new software, rather than the entire historical range. Nevertheless, this is an embarrassing development for Apple, given that watchOS updates are supposed to fix bugs, not introduce them.