It's possible that Excel has cached the metadata model.

You'll notice at the top of your OData document there is a link to a metadata document.

Excel and Power BI will download and cache this document, even if the document clearly states "do not cache me" in its response headers.

Once cached, any new columns will cause Excel to get upset at a new column appearing in the data document.

In Excel: Data > Get Data > Query Options > Data Load > Data Cache Management Options > Clear Cache.