Infinix Hot 2 (X510) on Android 6.0 doesn't show names when receiving a call
Based from Shelaf.com, you need to remove and re-add the Google Accounts and wait for them to resync.

Common Problems and Their Solutions
Problem 1: Contact not displaying names after making or receiving a call
Go to your Google Settings and remove all Google accounts. After some minutes, add them back and your problem should be fixed then.