Why has my iPhone and iPad stopped syncing data for contacts, reminders, calenders etc?

Hi WildOakDave,

Thanks for visiting Apple Support Communities.

It seems like iCloud is not syncing data between your iPhone and iPad. It can be hard to say why this happened, and troubleshooting can help isolate the cause of the behavior.

First, make sure the iCloud features you want to use on your iOS devices are turned on:

On your iOS device: Go to Settings > iCloud, then tap to turn on or off iCloud features.

From:

iCloud: Change iCloud feature settings

Next, try the troubleshooting steps in this article:

Get help using iCloud Contacts - Apple Support

Although the article only mentions iCloud contacts, the steps can also help if other iCloud services are not working as expected.

Sincerely,

Jeremy