After upgrading to CAS 6.3 we had received reports that case sessions are being invalidated every 24 hours. This could be related to the recent CAS 6.3.1 updated and requires investigation. These were also reported upstream: https://groups.google.com/u/0/a/apereo.org/g/cas-user/c/MkpgAZZn-Mw
To unbreak session storage we switched the memcached transcoder to the default Java serialiser. It's less space-efficient compared to Kryo, but it works fine.
We can revisit this in a future version and if the transcoder got fixed, revert back to Kryo.