I am getting a random warning with the following text:
The session id is too long or contains illegal characters, valid characters are a-z, A-Z, 0-9 and '-,' in...
In such cases $_COOKIE dump looks like this:
array (
'PHPSESSID' => '0t4qiq1ec36teca0l2ph74qq94,PHPSESSID=0t4qiq1ec36teca0l2ph74qq94,PHPSESSID=0t4qiq1ec36teca0l2ph74qq94,PHPSESSID=0t4qiq1ec36teca0l2ph74qq94',
)
Is it a bug or some kind of hacking attempt?
Edit The issue is gone after I've found an infinite redirect on the site under some conditions at the login page.