As of 436f10771 (make CommandStart return a StartMessage, 2019-06-06), find --json no longer outputs json.

For example, with

cd $(mktemp -dt gx-find-json-XXXXXXX)
git init && git annex init
echo one >one && git annex add one && git commit -mone
git annex find --json -- one

the last command outputs

one

rather than

{"bytesize":"4","mtime":"unknown","keyname":"2c8b08da5ce60398e1f19af0e5dccc744df274b826abe585eaba68c525434806","backend":"SHA256E","key":"SHA256E-s4--2c8b08da5ce60398e1f19af0e5dccc744df274b826abe585eaba68c525434806","humansize":"4 B","hashdirmixed":"0J/J1/","file":"one","hashdirlower":"171/8dc/"}

436f10771 appears to touch a lot of things, so perhaps other commands show similar issues and find is just the first I noticed.

On what operating system?

GNU/Linux, building git-annex with Guix

fixed --Joey