I have been seeing this issue on and off.
With structured output, I was seeing empty string, incomplete JSON and then full response for the same payload (in that order) for requests coming close to one after another.
With tools, I mostly saw response on the first request and subsequent requests for the same payload were returning either MALFORMED_FUNCTION_CALL or nothing in the content for the parts section.
As people mentioned here within the last 24 hours retries do not work as well as they did previously and there are more empty responses.