Contacts are not displaying after marshmallow update
I could fix this issue by doing the following steps.

First Wipe the Cache partition. (It won't erase any files or settings)

To wipe the cache partition do the following steps.


Ensure the device is powered off, and unplugged
Press and hold the Volume Down button and Power button (located on the right edge of the device) for approximately 3 seconds then release.  
From the "Boot Mode Selection Menu" screen, select Recovery.

Note: Use the Volume Down button to scroll through the menu options        and the Volume Up button to select.
From the "No Command" screen (Android figure lying on his back), press and hold the Power button, tap Volume Up once and then release the Power button.
Select "wipe cache partition".
Note: Use the Volume buttons to highlight and the Power button to select.
"Reboot system now" will be highlighted, press the Power button to select it.

Note: Allow several minutes for the reboot process to complete.


Once you are done with the Wipe procedure , go to https://contacts.google.com and export your contacts as .vcf file and copy to your device. 

Open Contacts App (Phone app) -> go to options on the top right corner (3 dots) -> choose import/export -> import from .vcf file. This will restore your contacts..