conflict save drafts

Hi,

we get following conflict when posts get saved as draft.

“Update failed. The response is not a valid JSON response.”

This ist just a failure message in the backend, without real effect, because drafts get saved in real.
Problem is, customer get confused for this message.

(See also the screenshot with german message)
https://ibb.co/SPS6YP7

How can we solve these conflict? Is there a possibillity to set an code snippet via snipet plugin to define a exception rule or other way?

Thanks