I haven't come across this before so I'm interested to solve this. Need more info though.
How much data are you saving in each session?
Do you have enough disk space where the /tmp directory holding the session files are?
How many files are in that /tmp directory (approximately before you erased them)?
How big was each file (or the biggest file)?
What version of PHP are you using?
What are you php.ini session related settings set to (like from phpinfo()😉?
Deleting the sess_xxx files from the temp directory will kill a users session.
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