As in the subject, desktop search works fine but when I click the result, it doesn't open. This seems to be specific to indexing results, since apps and other links open fine. A brief activity icon flashes in the taskbar but nothing launches.

Finally today found out the the problem is caused by a package wslu which is installed as a dependency of gimp-help-en. Uninstalling it fixed the problem.
More here https://bugs.launchpad.net/ubuntu/+source/systemsettings/+bug/1978842