PHP sinkhole #2: `$_SESSION` entries cannot have a key with pipes in it
Web at murray-mint dot co dot uk put this comment on the PHP
If you’re saving data to a session but finding it’s not actually being saved,
check and ensure that you’re not assigning any arrays with a key containing
the pipe character (|). This will prevent the session data from being
serialized and saved.
This bug is still in there six years later. And, while he didn’t mention it,
there is no error to indicate that it happened; it’s totally silent.