Pixel imported contacts' names not showing up at top of messages
After a long support session with Google, some combination of the following things resolved the issue: (although it was unclear what happened when because there were numerous glitches that occurred throughout the process which were corrected by clearing data and rebooting)


Force closing the contacts and Messages apps and restarting the phone
Clearing the cache of the Messages app
Clearing the data of the Messages app (note: this does not delete all your conversation threads as I feared it would. The warning may sound ominous, but at least for me, all my conversation threads were resynchronized following the data clearing and reopening the Messages app).
Going into settings of the Messages app, and changing the default SMS app to Hangouts, and then back to Messages (note #1: this requires the Hangouts app. note #2: upon opening Hangouts I was prompted to try the Messages app--I hit OK and this fixed >50% of my contact formatting issues)
Rebooting the device


This was on a Pixel with Android 7.1 and Messages 2.0.