I bought a Huawei Nova 2S while in China. Installed Google Play Services 14.3.66 (com.google.android.gms_14.3.66_(090408-213742215)-14366030_minAPI26(arm64-v8a,armeabi-v7a)(480dpi)_apkmirror.com).
I then downloaded many google apps (Google, Drive, Music, Gmail, Sheets, Keep, Maps, Hangouts, Youtube) but not all of them.
** Problem **: After downloading Google Contacts I cannot use the app. It asks me to sign in and when I attempt to do that I get "This account already exists on your device"
I have now upgraded to (com.google.android.gms_14.5.73_(040408-219655168)-14573021_minAPI23(arm64-v8a,armeabi-v7a)(480dpi)_apkmirror.com) but still no luck. I am going to post this on Google's contacts support website so will update this if a solution is found.
-I also checked the permissions for Gmail, Play services and Contacts. I selected "Trust this app" for all three to avoid any possible permission problems.
-Cleared app cache & data for Contacts. Re-started the phone but still no luck.
Some of the resources I've visited:
https://productforums.google.com/forum/#!topic/gmail/GO4l2n3k-1o;context-place=topicsearchin/gmail/This$20account$20already$20exists$20on$20your$20device$20contact - same issue but never solved.
https://productforums.google.com/forum/#!topic/gmail/USU0RXKwNds - again, unsolved
Next update: Removed google account, was able to sign in to contacts, but once in it didn't sync any data and acted like I never signed in at all with the sign-in button appearing at the top of the menu again.