Mail app stops sending notifications for Gmail (and others) when iCloud Contacts is enabled (macOS)

Hi everyone,

I’ve run into a strange issue on macOS and I’m trying to figure out if this is a known bug or if anyone else has experienced it.

As soon as I enable

System Settings → Apple ID → iCloud → Contacts,

the Mail app stops showing notifications for Gmail messages.

Here’s what happens:

• Gmail account is added in the Mail app
• Mail notifications are fully enabled (Banner/Sound allowed)
• Emails arrive normally (i.e. badge is visible), but no notifications are triggered
• “Important” or “critical” messages sometimes still trigger a notification
• If I turn off iCloud → Contacts, Gmail notifications immediately start working again

What I’ve tested so far:

• Completely removed and re-added the Gmail account
• Reset all Mail and Notification Center settings
• Full macOS reset → added only Gmail (without signing into Apple ID) → notifications work
• Signed into my Apple ID afterwards → issue returns instantly
• Focus modes are off

Extra context:

I have two Macs, and one was restored from a backup of the other. Not sure if that’s related, but the only fully reproducible trigger so far is enabling iCloud Contacts on the affected machine.

Question:

Has anyone seen this behavior before?

Is this a macOS bug, or is there some hidden setting tied to Contacts/iCloud that affects Mail notifications?

Thanks for any insight!