Known bugs in macOS Sierra 10.12: an incomplete summary

macOS Sierra 10.12 has now been available in final release form for a week. Here is a list of its bugs of which I am aware. Note that bad features, poor interface design, and problems with third-party apps, etc., are listed separately here.

Note: this list applies to Sierra 10.12. Following the release of the 10.12.5 update, I have transferred new bug reports (and existing ones) to the list for 10.12.5. This list is no longer maintained – that one is.

Kernel – Temporary breakdown in multitasking

Process scheduling in Sierra appears to break down occasionally. For example, when making a Time Machine backup via Thunderbolt (to a fast external RAID), the menubar clock and frontmost app may appear to freeze for periods of a minute or more, as the backup apparently hogs the hardware. If you leave the Mac alone (in particular, do not interact with keyboard or mouse/trackpad), normal multitasking resumes spontaneously – the clock starts ticking, and other processes are scheduled normally again.

The precise conditions needed to produce this are not clear. In my case a reproducible situation is to set MarsEdit a very heavy refresh task (1800 articles) from a WordPress blog. Throw a Time Machine backup in at the same time, and the CPU turns to porridge. But it doesn’t cause a kernel panic!

Core Foundation library – loss of drag and drop

After a certain period working in Sierra, attempts to drag and drop or otherwise cut/copy and paste content fail with a Core Foundation error -4960. In the case of drag and drop, this is likely to be the result of a memory leak, or similar. I have discussed this issue here. Once it occurs, the only way to restore normal function seems to be to log off and log back on again (or restart).

The frequency of this occurring diminished during El Capitan, but remains still in Sierra, although it may be confined to some older apps now.

About This Mac / Storage never completes

If you open About This Mac and select the Storage tab, the top bar should, after a while, display the disk usage on your startup volume. Many users are reporting that this remains stuck at Calculating…, and that one or more of the sections in the left of the Manage… dialog also remain busy and never report a size, even after 2 weeks. These appear to be bugs. No workaround has been discovered.

Console hangs

The new Console app can hang with a spinning beachball at times. The solution is to force it to quit.

log (command) – bugs in show options

Using log show, the --start and --end options, when used with a predicate, almost always result in a blank return, and do not find log entries which exist. Even used without a predicate, those options lose a lot of log entries. See this article for more details.

Workaround: don’t use --start and --end with predicates. Widen the time period when using --start and --end otherwise to lose fewer log entries. Try to use --last instead.

Finder aliases shown as documents

There is an intermittent bug in Sierra’s Finder which sometimes shows some aliases with the generic document icon. It should not affect their function as aliases (although it can sometimes confuse File Open and Save dialogs), so this appears cosmetic if irritating.

Installer may not work with some Core Storage LVG startup disks

Some users who have made their own ‘fusion drives’ using an SSD and hard drive, and then turned them into a Core Storage LVG using the diskutil command, report that the Sierra Installer app does not run installation properly on them. Although the first phase of the install runs, when the Mac restarts it drops back into El Capitan and the install fails. This is detailed here.

A workaround may be to make a bootable install USB stick, restart from that, and install. Further information is awaited.

Finder – incorrect column width

This can occur when using Finder windows which are set to column view. When switching folder in the view, the rightmost column being displayed has excessive width, filling the Finder window, its divider being placed incorrectly at the right edge of that window.


This long-standing but intermittent bug dates back to Mavericks if not earlier, and I have whinged about it here and here. It was also present in every version of El Capitan. The only workaround is to select a different folder, then to select the correct folder again.

Power Management – hard drives always put to sleep on system sleep

On some recent iMacs at least, Power Management ignores any setting to not put hard drives to sleep: when system sleep occurs, the hard drive in an internal Fusion Drive is always put to sleep, regardless of the drive sleep setting. This is detailed here, and was been present throughout 10.11.4-10.11.6.

The only workaround is to set the system sleep time to Never, which also stops hard drives from being put to sleep.

Energy Saver pane – inconsistencies in controls

The features available in the Energy Saver pane of System Preferences are inconsistent between Macs, and incomplete, for example not providing a separate control slider for system sleep on some hardware. Further details are here. These are unchanged in Sierra.

OS X internals – clicking on a window causes it to jump

When switching between apps by clicking on a window, sometimes the selected app comes to the front and its window jumps to a new position on screen. I used to think that this was confined to certain apps such as Tweetbot, but it also affects Apple’s Messages app, Finder windows, and others. These persist in Sierra, as they did in El Capitan.

The workaround is to switch to that other app by clicking on its icon in the Dock.

Trackpad – unexpected shift of text insertion point

This is another long-standing bug, which goes back to the early days of Apple’s Magic Trackpad in about 2010. You are typing along happily, with your hands well clear of the trackpad, and suddenly the text insertion point jumps to a different location in the text which you are editing. This is sporadic and completely unpredictable, but affects a wide range of different apps. This affected El Capitan very noticeably, and seems less common in Sierra, although it still does happen infrequently.

There is no workaround.

Audio output – spurious sounds on waking from sleep

Waking a system from sleep may result in two brief rumble sounds being output through analog audio channels. Preventing system sleep blocks this, of course.

Bugs in El Capitan which appear to be fixed (at last)

Sporadic freezing, requiring a forced or automatic restart: this turned out to be a new-style kernel panic, which became most common in El Capitan versions 10.11.4 to 10.11.6. It seems to have been largely resolved with the new kernel and extensions in Sierra, although infrequent semi-freezes most probably attributable to graphics driver and GPU problems can still occur.

Bluetooth, Magic Trackpad 2 – sporadic loss of connections: these affected the Magic Trackpad 2, and other Bluetooth devices. They appeared worst with Bluetooth Audio, which on some Macs effectively became unusable. These still occur infrequently, but seem to reconnect quickly.

Preview 8.1’s failure to work with high resolution images appears to be fixed in version 9.0 (Sierra).

Please add your own experiences and I will incorporate as necessary…

(Updated 19 October 2016)