After an upgrade, we might see the the user name shows 'undefined' on the upper right.
The problem is the cache not being updated after the upgrade.
Clarity PPM 15.x
To resolve this, clear the Clarity PPM cache.
Please, refer to this article for the complete information on how to clear the caches in Clarity PPM: 23812 - Clarity PPM: How to flush or clear the cache?
Similar problems might be encountered in the New UX. Refer to this article : 141041 - Avatar Displayed as 'Unknown' in the New UX