During Contact App usage an error pops up as "Contacts isn’t responding" in Galaxy Note 8?

Samsung is aware of this symptom which rarely appear on Note8 devices. Sometimes this could happen when certain applications were not updated to the latest version.

Samsung recommends following steps:

(A) Check if the Customisation Service application is updated to the latest version. (Latest version is 1.6.04.0 or higher)

Navigate to Settings →  Apps →  More →  Show system apps →  Customisation Service →  Check for current version 

Pictorial representation of the above settings are as follows :

1. Go to Settings and Tap Apps.

2. Tap More.

3. Tap Show system apps.

4. Tap Customisation Service.

5. Check for Customisation Service Version

(B) Update Software Version (If Software version is below 1.6.04.0)

Navigate to Galaxy Apps → More → My apps → Update → Tap Customisation Service → Update

Pictorial representation of the above settings are as follows :

1. Go to Galaxy App

2. Tap More and then Tap My apps

3. Tap Update

4. Tap Customisation Service

5. Tap Update

Also Samsung encourages users to keep software and apps updated to latest version, please check and update regularly.