The updateMemberships() method has this code:

// First, pull the current group roles.
$curRoles = $this->findCoPersonGroupRoles($coPersonId);

// And also the roles of $requesterCoPersonId, in case we need to check ownership
$requesterRoles = $this->findCoPersonGroupRoles($requesterRoles);

It should be this:

// First, pull the current group roles.
$curRoles = $this->findCoPersonGroupRoles($coPersonId);

// And also the roles of $requesterCoPersonId, in case we need to check ownership
$requesterRoles = $this->findCoPersonGroupRoles($requesterCoPersonId);