Unity's Dash is not searching files that I have opened before, only Applications. Neither Global nor Files lenses are showing any results.
In then Files lens, I can view most recent documents, but that's it.
I suspect it is caused by my home folder's encryption, due to errors displayed in /var/log/syslog:
[ 1868.382095] ecryptfs_encrypt_page: Error attempting to write lower page; rc = [-5]
[ 1868.382099] ecryptfs_writepage: Error encrypting page (upper index [0x000000000000000f])