Some Mac users are experiencing significant delays in receiving iMessages and SMS texts because of a bug affecting macOS High Sierra, as first spotted by AppleInsider. The issue reportedly also stops iCloud-connected devices like iPhones and Apple Watches from notifying users of received messages whenever the Mac is active.
One user wrote on an Apple forum, "I have to manually click the home button to see if I have received any messages. Only when i shut down the Macbook does the phone start responding with sounds + vibrations." For users affected, the only workaround seems to be completely disabling iMessage from their Mac, or downgrading to macOS Sierra. Other options, like disabling then reenabling iMessage, or sending a message on the Mac seem to only fix the problem temporarily.
The problem looks related to issues with syncing, as Apple planned to roll out Messages in iCloud on High Sierra. That feature would sync messages across every iOS device a user owns through iCloud — if you delete a specific message off your iPhone, for example, it'll also be removed from your Mac. The iCloud feature was planned to be included with the rollout of High Sierra but has been delayed until an update due later in the fall.
A community bug report has been created but the issue doesn’t appear to have been fixed in beta builds, according to AppleInsider. We've reached out to Apple for more details and will update this post if they respond.