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

If you are looking for a list of bugs in previous versions of Sierra, that for 10.12.5 is here, 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 Note, though, that those are no longer maintained.

Display sleep – multiple display setups may not wake properly after sleep

A few users, mainly with iMac 5K models, are reporting that allowing display sleep with one or more external displays connected causes problems when waking. Although the external displays wake normally, the iMac display does not. So far the only way to restore a normal image on the internal display is to restart. This was new with 10.12.4, persisted in 10.12.5, and fixed only for some users in 10.12.6.

The workaround is to disable display sleep if affected, and rely on a screensaver which darkens much or all of the display.

(Thanks to Richard Petersen for reporting this.)

Contacts – unexpected quit from Print dialog

Open the Print dialog in Contacts, and Show Details. With the uppermost popup menu reading Contacts (for the app-specific print settings), select the Style of Pocket Address Book. Almost any control which you try to adjust after that will result in an unexpected quit: for example, editing the Attributes, or changing the Flip Style. This was first noted here in 10.12.5, and is unchanged in 10.12.6.

There is no workaround: printing from Contacts remains partly broken.

Time Machine and other background activities – irregular and unreliable after long periods of running

The long-running bug affecting undocumented systems in macOS which schedule and dispatch background activities, most notably including Time Machine backups, has still not been fixed in 10.12.6. Macs which are left running continuously for more than about 7 days are liably to develop this. The most obvious symptom is that scheduled backups stop, becoming very irregular. Full details are here, and information about what has changed in 10.12.6 is here.

The only solution is to restart the affected Mac.

This bug was reported to Apple in February 2017. It has remained unfixed in 10.12.4, 10.12.5, and 10.12.6, although the last of those has brought some changes in the systems responsible.

Energy Saver pane – inconsistencies in controls, and misbehaviour on some models

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.

A further bug affects some models, including the iMac17,1 with a Fusion Drive: irrespective of the setting to put hard disks to sleep (ticked or not), system sleep invariably puts hard disks to sleep. The only way to prevent hard disks from being put to sleep is to prevent system sleep altogether.

These are long-standing issues which date back to El Capitan.

Preview – loss of all items from Services menu

Preview, and other apps which rely on PDFKit, no longer support any items in the Services menu. Those which had previously been accessible are no longer there.

There does not appear to be any workaround.

(Thanks to derdennis for reporting this.)

Mail – font sizing issues

Mail displays fonts of certain sizes incorrectly, and uses obsolete HTML markup for certain font sizes. This affects its main window, not the draft editor, and is detailed here.

There is no workaround.

(Thanks to Bart Hanson for reporting this.)

Mail – incorrect number of unread messages

Mail shows incorrect numbers of messages in the Unread or Flagged smart mailbox. This may be fixed by rebuilding the Mailbox.

(via Michael Tsai.)

Disk Utility – cannot handle APFS volumes

There are multiple issues in Disk Utility’s handling of APFS volumes. First Aid does not work on them, they are all reported as using the case-sensitive variant even when they don’t, and there is no support for APFS as an option in any of the app’s functions. See this article, which also explains why the command line is not a workaround either.

apfs_hfs_convert, diskutil apfs, newfs_apfs – fail to work properly

The suite of commands to support APFS no longer functions properly. At present, apfs_hfs_convert doesn’t complete the job with a container and volume, diskutil apfs commands to support the creation of containers and volumes have been removed, and the new substitutes in newfs_apfs do not appear to work. These are detailed here.

Additionally, mount doesn’t appear to handle freshly-made APFS volumes unless they are unmounted, then remounted.

The only workaround at present is to use 10.12.5, which does still have full functionality in this respect.

Disk Utility – commands fail

Various problems can be encountered in Disk Utility. This include an apparent inability to mount volumes, failure to partition disks, and sometimes reporting errors when trying to perform a command the first time, but performing them normally when asked a second time.

These are sporadic, and appear unpredictable.

(Thanks to Michael Tsai for reminding me of these.)

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 export the whole log to a .logarchive file, then browse that using Console. You may find it preferable to use my free Consolation, available from the Downloads item above, which provides sophisticated facilities for browsing log entries which have already been made.

log (command) – bug in collect option

The log collect --size option still does not restrict the size of log entries output – it is functionless and there is no workaround. This has remained unchanged since 10.12 initial release.

log (command) – bug in show option

log show returns log extracts which include entries of messageType Info irrespective of whether the --info option is specified. That option is therefore non-functional, and omitting it will not exclude Info messages.

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.

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

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.

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, but does still happen at times, particularly with Apple’s Messages app.

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

Bluetooth – spontaneous disconnections and others

Although much improved from El Capitan, and better for most than previous releases of Sierra, there are still problems which may be attributable to bugs in Bluetooth drivers, or perhaps in scheduling background activities. These include spontaneous disconnection of connected devices such as the Magic Trackpad 2. These are generally infrequent, and now seem innocuous: my iMac17,1, for example, suffered them every day in El Capitan and early releases of Sierra, but is now down to once every week or so. Your mileage may vary.

Previous bugs believed to have been fixed in 10.12.6

osascript open location now works in Terminal.

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

(Updated 5 August 2017)