I dont know if this is your issue or not but there is a bug in 2013 for using first / last name with , .
Its an ongoing problem. Could be why your getting the username to resolve but not the names themselfs!
as a user noted to microsoft:
Our Active Directory convention for the Display Name attribute is
"Last Name, First Name". Note the comma in between last and first
Our Logon names are based on people’s initials; these are 2, 3, 4 or 5
In SharePoint 2013, we experience problems in lists, with people
picker and with search refiners. It appears that the comma in the
display name is treated as a list separator.
When editing a list with a person field in grid-format, we are
experiencing these problems:
•You cannot enter a person through "Last Name, First Name". It throws
an error: “The user does not exist or is not unique” Some of our
colleagues have no “Last name”, hence no comma in their display and
those get validated without problems.
•You cannot copy a validated person with a Fill Down to other rows
•You can't look up a person with the people picker and select from the
search results. The selection does not pass validation in the grid,
but throws the error that the user does not exist, although it was
suggested by the people picker. (We assume that the person is passed
from People Picker to Grid component identified via the Display Name
string or the Distinguished Name attribute in which the comma is
•if you type a person’s "Last Name, First Name" and the First Name
corresponds to the Logon initials (DN attribute in AD) of another
person, then the other person gets selected.
•In search refiners, people names are shown with 2 comma’s instead of
1. “Last Name ,, First Name”
there are two resolutions.
1 use a script provided by microsoft to change:
first name , last name
first name last name
2 use this update:
Issues that this cumulative update package fixes
•When you assign a task to a user whose display name contains a comma
on a SharePoint Server 2013 site, you receive the following error
The user does not exist or is not unique.
also like to note that microsoft are not going to fix the issue as it would compramise other areas but it looks like the hotfix does solve the issue!