Hello Nat Harari,
Thanks for using Apple Support Communities.
I understand you're having an issue with the performance of the contacts app on your Mac. To get started with troubleshooting this issue I'd like you to please begin by booting into safe mode. Once in safe mode, try to replicate the issue. Note if the issue persists or not.
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Choose Apple menu > Shut Down.
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After your Mac shuts down, wait 10 seconds, then press the power button.
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Immediately after you hear the startup tone, hold down the Shift key.
You should press the Shift key as soon as possible after you hear the startup tone, but not before.
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Release the Shift key when you see the gray Apple logo and progress indicator.
To leave safe mode, restart your Mac again, but don’t hold down any keys during startup.
OS X El Capitan: Start up in safe mode
If the issue persists, then I suggest testing in a new user:
How to test with another user account
You can figure out if unexpected behavior is related to user file or setting by trying to reproduce the issue from another user account. This process includes creating a new user account, logging in to it, and testing for the issue.
Create a test user account
- From the Apple menu, choose System Preferences.
- Click the Users & Groups icon in the System Preferences window.
- Click the lock icon, then enter an administrator name and password.
- Click the Add button (+) below the list of users.
- Choose a type of user from the New Account pop-up menu.
- Give the user a full name, account name, and password.
- Click OK.
- Close the System Preferences window.
If there are documents from your original user account that you want to test with, place a copy of these items in the Shared folder in the Users folder. Press the Option key while dragging a file to this folder to create a copy.
Log in to the test user account
Log out of your current user account by choosing Log Out from the Apple menu, then log in to the new account you created. If you're prompted to sign in with your iCloud account or Apple ID when you log in, skip this step.
Try reproducing the issue
Try the same steps that caused the unexpected behavior to appear before. For example, if you were unable to print, try printing from this user account. If you were unable to connect to the Internet, try browsing a website from this user account.
If you were using any specific settings that testing depends on (such as using a specific email account or iCloud account) set up the same account in the test user. For email and most other settings you can use the Internet Accounts pane in System Preferences to set up these kinds of accounts. If files from your home folder are needed for testing, copy them to Shared folder in the Users folder (/Users/Shared). After logging in as the test user, copy these items to the same location in the test user's home folder to test with.
If an issue happens in only one user account
If performing the same steps in a test user account doesn't result in the same unexpected behavior, you most likely don't need to reinstall any apps or OS X.
- If an issue only happens in one app, check the app's documentation or support website for instructions on troubleshooting specific preference or setting files.
- If you need help with a specific alert message or issue, search the Apple Support website for the text of the alert message you're seeing.
If an issue happens in more than one user account
If the same unexpected behavior happens in more than one user account on your Mac, try checking for software or hardware issues.
How to test an issue in another user account on your Mac
Take care.