This can happen when one input's placeholder depends on the value of another input that lives in a different group. Hovering over the input whose placeholder references the other input's value causes the placeholder to disappear until the page is reloaded. This doesn't affect the input's actual functionality or any saved values.
What you might notice
An input's placeholder disappears when you hover over it
The placeholder only returns after refreshing the page
This happens specifically when the placeholder references the value of another input that's inside a different group
Workaround
Make the input's placeholder not depend on the value of the other input
Use a custom state on the page that updates when the referenced input's value changes, then set the placeholder to reference that custom state instead
Place both inputs inside the same group