The /var directory is not in the snapshots
See the exclusions
-in init (for the snapshots after installaion or update) line 1856
echo -e 'dev\nmnt\nproc\nrun\nsys\ntmp\nvar\n.fsckme.flg\nlost+found\nroot/.XLOADED\n.control' > exclusions1
-in /usr/local/easy_version/easy-version-control line 582
echo -e 'dev\nmnt\nproc\nrun\nsys\ntmp\nvar\n.fsckme.flg\nlost+found\nroot/.XLOADED\n.control' > /tmp/easy_version_control/snapshot-exclusions1
When you rollback, the directory .session is totally removed and recreated with the snapshot we return to (See /sbin/rollback in initrd)
So the content of /var is lost