Thanks for the proper details and the log-in information. I was able to track down the problem. Since the Search in post (and CPT) IDs? option is enabled on the General Options -> Sources panel, and the search phrase is empty, the search tried to match the post ID to an empty string – giving 0 matches all times.
I've fixed the problem directly, and marked it as a bug, will be fixed permanently in the upcoming release of course.Best,
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