“Month 13 is out of bounds” appeared in my Xcode console logs today. But I don’t do date arithmetics.

When you create an empty macOS Cocoa app from the template, the message shows, too. It’s emitted before applicationWillFinishLaunching(_:) is called.

Looking at the Console.app output of other processes, I saw this was all over the place. TextMate, loginwindow, User Event Agent – every app is triggering this message.

Rdar or GTFO, right? – rdar://35792221

Let’s hope this does not indicate any important framework part is broken.

This is both humbling and worrying. Humbling, because Apple engineers make just the same silly mistakes as us app developers. Worrying, because having a working macOS is rather important to a lot of people around the globe, and while this message does not prevent me from using my Mac or any apps so far, bugs like these could have people killed in other contexts (think aerospace or autonomous cars).

Getting Worse

Update 2017-11-06: (Yes, I’m back on Nov. 6th! :) Seriously, it’s now Monday, Dec 4th.) Like some other people I was suddenly suffering from 100% CPU usage by the process UserEventAgent which also consumed RAM at a rate of about 4GB/ every 3 minutes. Disk swapping galore, my Mac turned unusable quickly. Only way I found to get rid of this:

1. Deactivate automatic date and time setting
2. Reset the date back to something in November
3. Force quit the UserEventAgent process

Note that this only happened after rebooting. So if you can, do not shut down your Mac for a while just to make sure.