Lost all my contacts yesterday

Contacts are not saved in a backup. Contacts sync to email accounts (such as iCloud, AOL, gmail, MS Exchange, Outlook, etc), so if you delete an email account all of the contacts associated with it are removed. If you didn’t recently delete an email account open the Contacts app. Do you see Groups at the top left? Tap on it and make sure all groups are checked.

Contacts5321 Said:

"Lost all my contacts yesterday: How come I lost all my contacts"

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Two things:

Sign out of iCloud, and then back in. As for why you lost them, refer to the link provided atop this post.

How were you managing Contacts? Were they in iCloud? Have you logged into iCloud on a computer to see if your contacts are there? What were you doing when you lost these contacts?

Go to Settings/Contacts/Accounts. What accounts do you see? Did you delete any email accounts when adding Microsoft 365?

And what do you see when you open Contacts and tap on Groups?