Why does Migration Assistant freeze when cloning M3 to M4 MacBook?

Hi everyone,

I’m trying to migrate my data from my current M3 MacBook to a brand new M4 MacBook, but Migration Assistant keeps getting stuck no matter what I try. Hoping someone here can help me understand the cause or advise on a fix.

My setup & history

• Two years ago, I cloned an older Intel MacBook → my current M3 MacBook using Migration Assistant. That transfer worked perfectly.
• Now I’m trying to clone the M3 → new M4 MacBook.
• Data size is around 450–500GB.

What happens

• Migration Assistant starts, detects both Macs, and begins the process.
• On both machines, I get stuck on the “Starting up…” screen.
• If I click Back on the new M4 Mac, the UI becomes frozen (buttons do nothing).
• The old M3 Mac stays stuck at “Starting up” all night without progressing.

Troubleshooting already tried

• Connected both laptops directly to each other over Wi-Fi and also over the same network.
• Tried USB-C to USB-C cable connection.
• Restarted both Macs several times.
• Disabled firewall.
• Closed all apps.
• Left it running overnight (no progress).
• Verified both Macs are on the latest macOS version.

Any help, similar experiences, or solutions would be greatly appreciated!

Thanks in advance 

[Re-Titled by Moderator]

Original Title: Migration Assistant always freezes when cloning M3 → M4 MacBook (previously Intel → M3 clone). Any idea what’s wrong?