'acore' is the Contacts app (AKA, address book). I don't know what might have happened to cause this, but the solution could be as simple as going into the Manage apps section of Settings, and clearing cache of Contacts (followed by a reboot). If that doesn't resolve it, go back into Settings and clear cache and data, then reboot.
Note that clearing data will remove all entries and configuration customizations, so be sure you have a backup before proceeding, or be prepared to set everything up from scratch. Any Google contacts will automatically be backed up, but you'll still have to backup the app's data (e.g., using Helium).
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