One perhaps cosmetic bug gives insight into some bigger problems in Mail.
bugs
Lists bugs in macOS itself, not those manifest in third-party software running on it. Please report and I’ll keep the list updated.
How to diagnose this bug, manage it when it occurs, and try to prevent it from happening: latest information.
Lack of sleep can do strange things to people. Perhaps it can to Macs too. Could this solve the Time Machine irregularity bug?
Several bugs and issues in the log command will not result in errors, but will misleadingly return no log entries when used in search predicates.
Free, works with Sierra and other unified logs, examines log entries already in the log, unlike Console. Now supports logarchives and more.
When scheduled backups become irregular or stop, this affects much more than just Time Machine. This is what happens, and why you must restart.
How scheduling concurrent and background tasks using XPC Activity works, and compares with alternatives such as NSBackgroundActivityScheduler.
The good thing about the Sierra 10.12.5 update is that it seems to have caused few problems. But what did it actually address?
Tread carefully in the Print dialog of Contacts: its liable to cause an unexpected quit.
The Eclectic Light Company 