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Sorry to hear you’re facing problems 
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Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 18.0.2): 19.0.2
Operating system and version (eg, Ubuntu 20.04): Raspberry OS
Apache or nginx version (eg, Apache 2.4.25): Nginx 1.14.2
PHP version (eg, 7.1): 7.3
The issue you are facing:
In contacts app, I have a duplicate contact and it’s read only. I want to delete it, but can’t. When I click on the 3 dots there is no delete option. It’s a duplicate and I want it gone. This is my own server which is not shared with anybody else. It has one user, me so I want to remove this duplicate contact.
Is this the first time you’ve seen this error? (Y/N): Yes
Steps to replicate it:
Unsure, because unsure how the duplicate read-only contact got created. I didn’t create it.