The issue goes away when we disable the 'search' plugin.
We're running ikiwiki version 3.20180228-1.
+
+> Every time?
+> I used to see an error (this one, I think) intermittently on OS X, on incremental rebuilds only.
+> Haven't seen it in a while, though.
+> Maybe something got fixed upstream.
+> What OS, and what version of Xapian and Omega?
+> (1.4.11 for me.)
+> Maybe worth blowing away `.ikiwiki/xapian/`, as described in [[tips/inside_dot_ikiwiki]]?
+>
+> --[[schmonz]]
+>
+>> We've removed the `.ikiwiki/xapian` directory before performing a rebuild, including actually rebooting the host OS. The search appears to work for a while, but once the wiki has been live for a while (and subject to edits on the web interface), the issue reappears.
+>>
+>> * OS: Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-47-generic x86_64)
+>> * xapian-tools/bionic-updates,bionic-security,now 1.4.5-1ubuntu0.1 amd64
+>> * xapian-omega/bionic,now 1.4.5-1 amd64
+>>
+>> I've upgraded our installations of both Xapian components and will let you know if that fixes it.
+>> -- jsewell
+>>
+>>> Updating appeared to fix it. Sorry for not trying that sooner. Thanks for the help.
+>>> -- jsewell