Advanced Search via API not working properly

The developer documentation shows Advanced Search via the API - with examples including:

https://api.deezer.com/search?q=artist:"aloe blacc" track:"i need a dollar"

It currently only returns

{"data":[],"total":0}

This used to work well - so something has changed or is broken.

Documentation is at https://developers.deezer.com/api/search