Could be related to random problem. There has been a lot of discussion about this in the past versions:
Search for episerver store was queried with a [string].
Here's an example:
the UI makes a lot of Ajax requests to the server. if a request failed but it's only one time thing, it will be fine in 99.99% cases. if it's consistent then you might have a problem, but I'd say ignore it if you don't have any implication on features, and if you see nothing strange in your application log.
I am working on this new CMS 12 application and see a lot of this error in console. There doesn't seem to be an impact on application itself or may be something I am not seeing.