Sharepoint Online Advanced Search Date Filter Fails

Using Sharepont Online Search Center Advanced Search, when specifying a Date for an On or After Date search, I am getting a peculiar "We aren't sure we understood your query"... error, and twice the number of returns than the site actually contains?

Returns the following:

When filtering a return set in the Library views area of the same site using the Key Filters refiners, the same Date query appears to work fine (so the syntax would appear to be correct)

What do I need to do to not confuse the Microsoft Search Center?

Most likely the error:

We're not sure we understood your query, so the results might not be what you were looking for.

occurs since a custom managed property named LastModDate has not been configured or(and) not available in search results (see Solution section below).

The point is Key Filters refiners results (latter screenshot) are query based , while the results displayed in search page (first screenshot) are search based, it means the results are retrieved from different data sources.

Solution

To utilize LastModDate managed property in search results:

• ensure LastModDate Managed Property is configured properly. Follow Create a new managed property for a instructions

• to make sure that your changes are crawled and re-indexed, you can specifically request a re-indexing of the list or library. When you do this, the list or library content will be re-crawled and re-indexed so that you can start using your new managed properties in queries, query rules and display templates. Follow Re-index a document library or a list section for a more details.