Searching result gone sometime and then automatically resolve

I put some documents in different folders on SharePoint (all files has a common customeize property. e.g. Prop_1 with value "ABCD").

And then I search documents through API with keyword "ABCD". Those folders and document are able to show in search result. But sometimes they disappear without editing anything. And usually, those documents / folders appear in search result in next 3-4 hours without doing anything.

Any settings or config can resolve for this? or this is a bug of SharePoint?