Contacts information disappears

Hey George Perides,

Thanks for posting in Apple Support Communities. There's some great guidance in related article, If your iCloud Contacts, Calendars, or Reminders won’t sync - Apple Support so we'd recommend starting with the basics there.

"Things to check first

1. Check the system status of iCloud Contacts, Calendars, or Reminders for services outages or connection issues.
2. If a reminder isn't showing up on some of your devices, make sure that your iPhone and iPad have the latest version of iOS or iPadOS, or that your Mac has the latest version of macOS.
3. Make sure that you're signed in to iCloud with the same Apple ID on all of your devices. Then, check that you turned on Contacts, Calendars, and Reminders in your iCloud settings.
4. Check that the date and time settings on your device are correct for your current location."

Also, since your contacts may be related to iCloud or a third-party account, it may be best to set iCloud as default. The following is from the same article mentioned above. Check out the Mac sections as well.

"In iOS 15 or earlier:

1. Open the Contacts app and tap Groups in the upper-left corner.
2. Deselect the All [account] option for any third-party account, like Gmail or Yahoo.
3. Make sure All iCloud is selected.
4. Tap Done to see your list of contacts. If you don't see the contact you're looking for, it's stored in another account.
5. If you have a copy of your contacts from a third-party service in vCard format version 3.0 or later, you can import the contacts into iCloud.

Set iCloud as the default account for your contacts:

1. Tap Settings, then Contacts.
2. Tap Default Account.
3. Select iCloud."

All the best.