ios12 reminders iCloud not synchronizing

Try these steps first

Make sure that iCloud Contacts, Calendars, and Reminders are available. If there's an issue, try again after it's fixed. If there isn't an issue, try these steps.

Remember to back up your contacts, calendars, and reminders, so you don't lose anything.

After each step, see if you still need help:

1. Check for updates to your iPhone, iPad, iPod touch, Mac, or PC. To use iCloud, your devices need to meet the system requirements.
2. See if the date and time settings on your iPhone, iPad, iPod touch, Mac, or PC are correct.
3. Make sure that you're signed in to iCloud with the same Apple ID on all your devices and check your settings.
   • On your iPhone, tap Settings > [your name] > iCloud. If you're using iOS 10.2 or earlier, tap Settings > iCloud. Check your Apple ID and make sure that you turn on what you want to update (Contacts, Calendars, or Reminders).
   • On your Mac, choose Apple menu > System Preferences > iCloud. Check your Apple ID and make sure that you select what you want to update (Contacts, Calendars, or Reminders).
   • On your PC, open iCloud for Windows. Check your Apple ID and make sure that you select what you want to update (Mail, Contacts, Calendars, and Tasks).
4. If you sign in to third-party apps with your Apple ID, protect your account with two-factor authentication and use an app-specific password. If you don’t have devices that can be updated to iOS 9 or OS X El Capitan or later, you can set up two-step verification instead.
5. Open Safari and go to www.apple.com to check your connection. If you can’t open the page, get help connecting to the Internet.
6. Open a secure website, like your Apple ID account page, to see if you can access port 443. If the website won't open, contact your Internet service provider for help. Safari needs access to port 443 to update your information in iCloud.
7. Keep your data within the limits. If you go over the limit, your data won't stay up to date.

Set iCloud Contacts, Calendars, or Reminders as your default

See which account your reminders are in:

1. Open the Reminders app and tap the list name in the upper-left corner to view all your lists.
2. See if the list is stored on your device or iCloud. Open a list and tap Edit. If you see Sharing, then your list is in iCloud.

When you create a reminder, you can choose to store it in iCloud or on your iOS device.

Change how often your calendars and reminders update:

1. Tap Settings > Calendar, or tap Settings > Reminders.
2. Tap Sync.
3. If All Events or All Reminders is selected, choose a specific timeframe instead, like Events or Reminders 1 Month Back. If a specific timeframe is selected, choose All Events or All Reminders instead.
4. Press the Home button.
5. Wait a few minutes. Open the Calendar app, tap the Calendars tab, and swipe down to refresh.