"Cannot read property 'kind' of undefined" when searching for a word to add to a level

When trying to search for a word from the DB to add to a course level nothing happens and the console throws an error.

The course is this one: https://www.memrise.com/course/1557945/jp4-kanji-para-recordar-i-heisig-japones/edit/

This is the console error:

Uncaught TypeError: Cannot read property ‘kind’ of undefined
at Object. (memrise-bundle-6a2501c87.js:2)
at Function.each (libs-38c180b77.js:1)
at Object.get_thing_context (memrise-bundle-6a2501c87.js:2)
at editing-b58046687.js:2
at Function.an (libs-38c180b77.js:4)
at i.getContext (editing-b58046687.js:2)
at i.render (editing-b58046687.js:2)
at initialize (editing-b58046687.js:2)
at new i (libs-38c180b77.js:9)
at Object.success (editing-b58046687.js:2)
(anonymous) @ memrise-bundle-6a2501c87.js:2
each @ libs-38c180b77.js:1
get_thing_context @ memrise-bundle-6a2501c87.js:2
(anonymous) @ editing-b58046687.js:2
an @ libs-38c180b77.js:4
getContext @ editing-b58046687.js:2
render @ editing-b58046687.js:2
initialize @ editing-b58046687.js:2
i @ libs-38c180b77.js:9
success @ editing-b58046687.js:2
c @ libs-38c180b77.js:2
fireWith @ libs-38c180b77.js:2
n @ libs-38c180b77.js:3
(anonymous) @ libs-38c180b77.js:3