IOERROR: conversations_audit on store

I am using Cyrus 3.2.2 on Debian Buster 10 (package from buster- backports). I am having lots of errors similar to these in the logs: cyrus/imaps[24052]: IOERROR: conversations_audit on store: /var/lib/cyrus/user/e/example.conversations Bff62cd0852db22e1 0 (1452110 1 0 0 () ((1 1452109 1 1 0))

Xapian index not being used for message search in Roundcube

I have configured Cyrus 3.0.13 with the Xapian search engine and enabled search_fuzzy_always. This appears to work fine when I search in the message body using the Evolution mail client, as I get a response quickly: <15824537091582453713>* SEARCH 226927 226929 226964 226974 226999 227215 227238 [.