Create a 16.5.0 instance, using the same URL as a 16.4.0 one you used just before.
Using the in-place editor, clicking on "save" empties the page instead of saving the new content. The problem vanishes after clearing the cache.
The problem re-appears after stopping the 16.5.0 instance, starting the 16.4.0 one, clearing the cache, editing the page with the in-place editor, and then switching again to 16.5.0.
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