Monitor flickers on macOS Sequoia after sleep wake cycle

When does this happen?

You close your MacBook lid or let your Mac go to sleep. When you wake it up—by pressing a key or moving the mouse—the external monitor flickers. Not just a quick flash. It stutters, flashes black, or shows static for a few seconds. Sometimes it never settles, and you have to unplug and replug the cable.

I see this with macOS Sequoia (15.0 and 15.1) on MacBook Pros with M2 Pro and M3 Max chips. It also hits Mac Studio users with Apple Studio Display or third-party 4K monitors. The triggers: waking from sleep after 30+ minutes idle, or switching between clamshell mode and open lid.

What's actually causing the flicker?

Two things, usually working together:

1. Refresh rate mismatch. macOS Sequoia sometimes forgets the monitor's preferred refresh rate after sleep. The GPU tries to push 60Hz, but the monitor stays stuck at 59.94Hz or 30Hz. They fight, and you see flicker.
2. Bad cable handshake. USB-C to DisplayPort cables with poor shielding or older HDMI 1.4 cables can lose the HDCP handshake after sleep. The display goes black briefly, then renegotiates.

The good news: it's rarely a hardware failure. Your monitor is fine. Your Mac is fine. It's just macOS forgetting the handshake.

Step-by-step fix

Step 1: Replace your cable (the real fix)

I know you want to try software first. Skip it. Do this step now. Grab a certified DisplayPort 1.4 cable or a USB-C to DisplayPort 1.4 cable that supports 4K at 60Hz. If you're using an included HDMI cable from a Dell or LG monitor, toss it—those cheap cables are notorious for this exact issue.

Plug the new cable directly into your Mac's Thunderbolt 4 port. Not through a hub or dock unless you know the dock is Thunderbolt 4 certified. Docks add another handshake step and more places for things to go wrong.

Step 2: Lock the refresh rate

1. Open System Settings > Displays.
2. Click your external monitor.
3. Set Refresh Rate to 60Hz (not "ProMotion" or "Variable").
4. If you don't see 60Hz, hold the Option key while clicking the refresh rate dropdown. That shows hidden modes. Pick 60Hz.
5. Close System Settings.

This forces macOS to stick with 60Hz instead of negotiating a variable rate after sleep.

Step 3: Disable True Tone (if using MacBook)

True Tone on your MacBook's built-in display can confuse the external monitor's color profile after wake. Turn it off:

1. Go to System Settings > Displays.
2. Uncheck True Tone.
3. Do this for both the built-in display and the external monitor (click each one in the sidebar).

This stopped the flicker for two of my readers last week.

Step 4: Reset the display settings (nuclear option)

If steps 1–3 don't work, macOS might be holding onto a bad display profile. Delete it:

1. Open Terminal.
2. Paste this command and press Enter:

sudo rm -f /Library/Preferences/com.apple.windowserver.plist

3. Enter your admin password if prompted.
4. Restart your Mac.

This clears the cached display settings. macOS will rebuild them when you plug your monitor back in. Expect a slight resolution reset—you'll need to re-check "Scaled" resolution afterward.

What to check if it still flickers

If you're still seeing flicker after all this, check these:

• Is your monitor firmware up to date? Check your monitor's OSD (on-screen display) menu under "Information" or "Support". Some Dell and LG monitors have firmware updates that fix HDCP handshake issues with macOS Sequoia.
• Do you have an app called "MonitorControl" or "BetterDisplay" installed? These third-party tools can override refresh rates after sleep. Uninstall them temporarily to test.
• Are you using a Sonnet or CalDigit hub? Some Thunderbolt 3 hubs had known handshake issues with M-series Macs. Try going direct to the Mac.
• Is it only flickering when you open a full-screen video? That's a different problem—it's likely an HDCP handshake failure. Try a different HDMI port on the monitor (sometimes port 1 is stricter).

And—I hate to say it—if you're on macOS Sequoia 15.0 and none of this works, consider reverting to macOS Sonoma. Apple fixed a similar flicker bug in Sonoma 14.6, and Sequoia 15.0 reintroduced it. I expect a fix in 15.2, but if you need a stable machine today, go back.

We've all been there. You're not alone. Try the cable first. I bet it works.