Mac OS 27 Problems and Bugs

If Resident Evil is running slow on your MacBook Air, and other programs are lagging as well, it is possible there are processes running in the background that are using significant resources. Check Activity Monitor, CPU tab (sort by % CPU) and Memory tab (sort by Memory) to see what's running hard.

Activity Monitor User Guide for Mac - Apple Support

Confirm that you have sufficient free space on your internal storage. The absolute minimum is ~20-25 GB free space, and as a rule of thumb you should aim to have 15-20% of your total internal storage as free space. You can check the amount of free space you have on your Mac in a variety of ways:

• • Select your internal drive then click File menu > Get Info, check Available space
  • Go to System Settings > General > Storage, check the graphical display at the top of the settings pane
  • In Disk Utility (in Applications > Utilities), by selecting the main container disk below the drive itself (you may need to select View menu > Show all devices to see it)
  • In the System Report – hold the Option key and click the Apple menu > System Information (the top menu item), look for the name of your internal drive (Macintosh HD, unless you have renamed it as I did)

Some steps to take to safely free up space:

Free up storage space on Mac - Apple Support

Optimize storage space on your Mac - Apple Support

How to free up ‘System Data’ and other st… - Apple Community

If nothing in the above reveals an obvious culprit, then appropriate troubleshooting steps are Safe Mode and creating a new user account to test. 

See if the problem is present when you boot in safe mode. That process performs some system cleanup and clears caches, and also disables 3rd party extensions that may cause problems.

Start up your Mac in safe mode - Apple Support

If that does not correct the issue, test in a new user account. A newly-created user account will have all settings at default, and if the issue does not occur in that new account then it provides guidance on what may need to be changed to correct the issue.

Add a user or group on Mac - Apple Support

Once the testing is complete, the new account can easily be deleted.

Delete a user or group on Mac – Apple Support

If you have 3rd party ‘protection’ software installed, that may be the problem. That includes:

• Cleaners (software claiming to automatically free up space)
• Optimizers (software claiming to make your Mac run faster)
• Antivirus software
• VPN software (unless provided by a school/employer to enable access to internal resources from a remote location)

Such 3rd party system ‘helpers’, ‘cleaners’ and ‘protectors’ do more harm than good. In fact, such products are completely unnecessary for macOS and the only ‘good’ (if you want to call it that) they do is to put money in the developers’ pockets. Cleaners and protectors cause compatibility issues, often after macOS updates. Commercial VPNs claim to hide your browsing activity from websites, and while that may be true those VPN providers just sell your browsing data to others. For the user, all of these types of software offer only harm…and if that is limited to harm to your bank account, then count yourself lucky. If you have installed such software, follow the developer’s instructions to completely uninstall it (note that some developers fail to provide instructions and their software installs can be pervasive, meaning the only way to truly remove it is to erase your Mac, reinstall macOS then restore your user files from a backup).

It might help to download and run EtreCheck, written by a long-time forum member. The free version is fine. Post the full report using the Additional Text button. No personal information is revealed. 

Part 1 of 2

Since all of these problems started after upgrading your 13-inch M5 MacBook Air with 16 GB of memory from macOS 26 to macOS 27.0, 

I would start by installing the latest available macOS 27 update and restarting the Mac. 

Apple recommends keeping macOS up to date because updates can include bug fixes and other improvements. Update macOS on Mac

Before testing Resident Evil again, check System Settings >> General >> Storage to make sure there is sufficient free space. 

If the game starts slowing down while the Mac is still responsive, open Activity Monitor and check CPU usage and Memory Pressure. 

That may provide useful information about what is happening when the slowdown begins. View Activity Monitor on Mac

The Resident Evil issue is particularly worth documenting because you report that it previously ran for 1–2 hours without the problem under macOS 26, but now slows down after about 15 minutes under macOS 27 and eventually leaves the Mac unresponsive before it shuts down. 

Since the Mac is shutting down unexpectedly, disconnect any non-essential external devices and test again.

If it still shuts down, run Apple Diagnostics. If your Mac restarted because of a problem  Use Apple Diagnostics to test your Mac

It would also be useful to test the Mac in Safe Mode. Apple says Safe Mode can help determine whether software that loads during startup is contributing to a problem. 

For the Mission Control lag, try it immediately after restarting, before opening Resident Evil or another demanding application. 

That may help show whether the problem occurs independently of the game.

For Safari, since other websites work but YouTube does not, first try YouTube in a Safari Private Window. 

Apple also recommends checking Safari extensions, website data, Private Relay, VPNs, and other network or security software when a particular website does not work correctly. If Safari doesn't work as expected on Mac

If YouTube still does not work, try the same video in another browser on the Mac. 

If possible, also try YouTube on another device using the same internet connection. That can help narrow down whether the problem is specific to Safari or involves YouTube or the network connection.

At this stage, I would not assume that all of these problems have one cause, that macOS 27 is responsible for every symptom, or that the shutdown is caused by heat. 

There is not enough information yet to establish any of those explanations. 

If the Mac shuts down again, note exactly what happens immediately beforehand and whether macOS reports that the Mac restarted because of a problem. 

Any Apple Diagnostics result or other diagnostic information would also be useful.

Overall, the fact that the problems appeared after the macOS 27 upgrade is important, but the individual symptoms should be tested separately so the actual cause can be narrowed down rather than assumed.

Part 2 of 2

To avoid a game of 20 questions   

Download the Application Etrecheck  ( External Link ) directly from the Developer.

This is a Diagnostic Tool that makes no changes to the computer.

It makes a coherent and readable inventory of both the Hardware and Software used on the computer 

The application is free or paid for added features. 

The Report will Not Reveal Any Personal Information. 

Post back the Full Report - Share Report >> Copy , then  paste  >>>> using the Additional Text Icon  <<<<