Note that bad features, poor interface design, and problems with third-party apps, etc., are listed separately here.

Following the release of Sierra 10.12.6, this list has been superseded by the new list for 10.12.6. This list is no longer maintained: please refer to that last for the latest information.

If you are looking for a list of bugs in previous versions of Sierra, that for 10.12.4 is here, for 10.12.3 is here, for 10.12.2 is here, for 10.12.1 is here and for 10.12 is here. Note, though, that those are no longer maintained.

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 report 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 months. These appear to be bugs, and have been present since 10.12. No workaround has been discovered.

Time Capsule – error -36 when accessing files

Some users are encountering -36 errors when they try to access files on Time Capsules, and possibly other forms of networked storage. These occur when accessed using normal AFP protocols, e.g. via afp://devicename This appears sporadic and not general: many other users find that 10.12.2 is better behaved than 10.12.1 was, particularly when using Time Machine.

Workaround: use SMB rather than AFP, by pointing the Finder’s Connect to Server command at smb://servername/sharename instead.

Thanks to Mark for reporting this in the comments here.

Power Management – sleeps despite Energy Saver settings

Long-standing bugs in Power Management continue. Despite Energy Saver pane settings intended to prevent system or hard disk sleep, sometimes a Mac may still decide to go to sleep, including powering hard disks down. This appears to be ‘normal’ sleep, and the Mac still wakes up normally. Details including log excerpts are here.

There is no workaround.

Console – no access to full historic log data

The Console utility does not provide full access to log entries already gathered before the app is opened. This has been the case since Sierra 10.12.

Workaround: use the log show command in Terminal, or LogLogger5d from here.

log (command) – bugs in show and collect options

Using log show, the --start and --end options now work better than in 10.12, but still do not discover all log entries in the specified time period, or may use an incorrect time period. Widening the time window will normally result in discovering more entries in any given period.

Workaround: widen the time window specified by --start and --end, or use --last instead.

Additionally, the log collect --size option still does not restrict the size of log entries output – it is functionless and there is no workaround.

Recovery mode – may require a wired USB keyboard to enter

Prior to macOS Sierra, it was usually possible to enter Recovery mode, holding the Command and R keys during startup, using a wireless keyboard. Trying to do the same in Sierra 10.12.1 or 10.12.2 may fail, and normal startup proceeds.

Workaround: use a wired (USB) keyboard, or connect an Apple Magic Keyboard using its charging cable.

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.

Finder – inconsistencies and other bugs in List views

There are several bugs in the Finder’s handling of maximize (zoom), which are most prominent, and perhaps largely confined to, List views. The most obvious, reported here, is that maximising List views often doesn’t result in a window which is deep enough to contain all the items in the view, even though there is ample space to do so. Various other issues have been reported – see the comments to this article for fuller details.

Although these don’t have major impact, and can be worked around, they are messy and inconsistent.

System Integrity Protection (SIP) – zero-day vulnerability

There is a zero-day vulnerability in El Capitan’s and Sierra’s SIP which could be locally exploited. Further information is here, and full details here.

As this cannot (yet) be exploited remotely, users should be wary of this potential for local attack. Although awaiting confirmation, there is nothing in the security notes to suggest that this has been fixed in 10.12.2.

App Store – dysfunctional behaviour

There are still occasional issues with the App Store app 2.2, although these have not been as florid or as frequent as in previous versions. Details are here.

There is no workaround, of course.

Finder and file system (HFS+) – strange behaviours with ~/Library/Mobile Documents

The ‘folder’ ~/Library/Mobile Documents cannot be opened in the Finder, but redirects to iCloudDrive. The odd behaviours associated with this are detailed here, and are not bugs but ‘features’. The workaround is to access them via Terminal, as detailed in that article.

Apple Magic Keyboard – duplicated letters

Sometimes, when typing normally, letters are incorrectly duplicated although if the key had been held pressed for too long, that would not have resulted in keystroke repeat, but would have popped up the accented character picker. This has been a sporadic problem since El Capitan and persists in Sierra.

I suspect the workaround is to use a wired keyboard.

Bluetooth – spontaneous disconnections and others

Although much improved from El Capitan, there are still problems which appear attributable to bugs in Bluetooth drivers. These include spontaneous disconnection of connected devices such as the Magic Trackpad 2, loss of Continuity features on some models, and the incompatibility with Boot Camp of some recent MacBooks noted above. These are generally infrequent, and very unlikely to result in kernel panics (unless those in El Capitan). Further details are here.

Power Management – removal of the ‘Time Remaining’ estimate of battery endurance from recent MacBook Pro models.

This is apparently because of inherent inaccuracies in its forecasts. This information remains available from the Terminal command
pmset -g batt
and from several utility widgets such as iStat.

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. This long-standing bug, which persisted through versions of El Capitan, now seems to occur less frequently in 10.12.2, but does still happen at times.

With the Messages app, in 10.12.2, when you first switch to the app by clicking on its window, you may be unable to place the insertion point of the cursor in its text editing box, but have to click on the head of the window, which then causes the window to jump to a different screen location. Only then can you start editing a new message.

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

security (command) – show-keychain-info writes its output to stderr

The security show-keychain-info command and verb do not return their results to standard output, but to standard error. This may apply to other verbs (not tested). The path supplied also has various issues with supplied path strings, which may result in errors. Further details are here.

Workaround: collect its output from the standard error stream when calling from other code.

Previous bugs believed to have been fixed in 10.12.2

FileVault – a nasty vulnerability which allows password recovery has been fixed. Further details are here. Download my free LockRattler tool from here to check your Mac.
Boot Camp – broken on recent MacBook models running 10.12.1.
Finder aliases shown as documents.
Time Machine backups to USB3 drives – unreliability, often fail to complete.

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

(Updated 24 January 2017)