Ray Maker wore an Apple Watch Ultra 4 on one wrist and a Series 12 on the other, ran eight 600 meter repeats on a track, and watched the two watches disagree about how tired he was. The Series 12 dropped his Readiness score from 5 to 3 straight away. The Ultra 4 showed nothing at first and caught up about two hours later, landing on 3 as well.

Maker published that in his Ultra 4 review at DC Rainmaker on September 17, and he writes that Apple has told him it is working on it and hopes to have fixes shortly. That is his account of what Apple said to him rather than anything Apple has published, and it carries no watchOS version and no date.

His Series 12 showed a sleep score on the iPhone immediately, then refused for four hours to show the same score on the watch, and with no sleep score there was no Readiness score either. Both appeared at once in the end. He also saw fields come up blank and fill in a second later, and wrong values correct themselves a few seconds after that.

Readiness gives you a number from 0 to 10 and one of four labels: Recover, Pace Yourself, Ready, or Go for it. It is supposed to move as your workouts, sleep and vitals move, and the point of it is to check it before you decide how hard to train. A score that sits still for four hours after a night's sleep is answering a question you asked yesterday.

Readiness needs seven nights of heart rate variability data, with at least four hours of sleep a night, before it will show you a first score at all, and each watch builds that history on its own. Plenty of people are in that first week right now. Maker's watches were not. They already had scores, and the lag happened anyway.

He offers no workaround, and on his watches the score always turned up eventually. If yours looks stuck after a workout, the watch may simply not have caught up. Check the Readiness section of the Fitness app on your iPhone before you decide the number is wrong, and don't read much into a figure that changes within seconds of you opening it.

He calls Apple's implementation pretty solid and close in broad strokes to Garmin's, with Garmin more responsive at this point, and he hopes the delays are a one-off fluke. He plans to put Apple's scores up against other brands in a week or two. This is one reviewer's pair of watches over a few days, so nobody can say yet how many owners see the same thing.

Apple told him it hopes to have fixes shortly. It has not said so anywhere its customers can read it.