TYPO3 Core

I am noticing very strange behavior using sr_feuser_register and felogin. After a successful login, I show a welcome message at the top of the screen, stating
"You are current signed in as Mr/Ms ###LAST_NAME###". What is odd is that sometimes the wrong last name is show for the logged in user. Taking a look at the database, both users were indeed signed in at the same time. Even odder is that sometimes the information is correct. I had flushed all cookies, frontend session data, etc. but the problem persists. I am not sure if this is a problem with felogin, the sr_feuser_register extension, the core, or simply my implementation.

The greeting message is created in the typoscript:

lib.userMessage = TEXT
lib.userMessage.value = You are currently logged in as {TSFE:fe_user|user|username}.

What could be causing this?