TYPO3 Core

We're currently working hard to bring powermail back to live in 12. One obstactle seems to be the session handling. In 12 all captchas are not working any more.

What we see was, that this code seems not to work any more:

# Create "fe_typo_user" cookie and store a value in the related database table
$GLOBALS['TSFE']->fe_user->setKey('ses', 'foo', ['foo' => 'bar']);

Can you please tell us what we're missing here?

Addition: So it's not possible to read the value when page is reloaded with:

$GLOBALS['TSFE']->fe_user->getKey('ses', 'foo');