Why won’t my Mac sleep after I unplug a display with sleep prevention enabled?

Check which process is still preventing sleep. BetterDisplay’s per-display sleep prevention should be released when that display disconnects, but another display, app or macOS activity can continue to keep the Mac awake.

To compare the states, temporarily turn off sleep prevention for all displays, wait at least 15 seconds, and run this read-only command in Terminal:

pmset -g assertions

Then enable sleep prevention for one connected external display, wait at least 15 seconds and run the command again. Finally, unplug that display, wait again and repeat the command. Keep the three outputs so you can compare entries under Listed by owning process.

Look for an entry owned by BetterDisplay with a name such as Prevent system sleep for device with tagID …. It should appear while that display’s prevention is active and disappear after it disconnects. The tag identifies the display record. It is not a process ID.

A separate entry named Prevent system sleep during an operation protects brief display changes such as a mode switch or reconnection. It normally expires about 10 seconds after the last such operation. Repeated operations can extend it, so compare after the display arrangement has settled.

If BetterDisplay’s entries disappear but the Mac still stays awake, inspect the remaining entries and their owning processes. A system-wide sleep-prevention value of 1 does not identify BetterDisplay as its source. Some entries have timeouts, so one snapshot does not establish a lasting fault.

If BetterDisplay’s per-display entry remains, check whether another connected display has sleep prevention enabled and whether the unplugged display is still shown as connected. Retain the before-and-after outputs and the display state for diagnosis. The command observes sleep assertions. It does not force sleep or change power settings.