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Hi @Speedy1981,
Welcome to the community.
If the issue does not persist in safe mode then it will be some conflict with a third party application. It could be Facebook as you suggest. The only way to be sure would be to start uninstalling apps one at a time and testing after each one.
I'm having the same issue. The issue started once I'd upgraded to Marshmallow. I can search using the Sony Contacts app but cannot edit, as soon as I edit it crashes. The Google Contacts app is worse, as soon as I type a character it crashes. Therefore cannot add or edit any contacts on my Android handset using Google Contacts.
I'm sorry to hear that 
It might be a 3:rd party app that's synchronizing contacts and is not working as it should. Go to Settings -> Accounts and see what accounts you have there and which that has the option to synchronize contacts. Try removing these and see if that helps.