Why's there "no data" appearing on some patents' pages on Patent Search?

Current availability of a patent's data can vary from country to country.

You can refer to the Data Collections link, where the Patent Document Coverage tab can lead to the patent data availability of individual countries (Asia and Euroasia, Europe, the Americas, & Africa, Oceania and Others)

Take Austria for example: the following illustrates that Austrian patents come with data of Bibliography, Abstract, Citations and Family. The other information such as Claims, Spec., Drawings and PDF is not available, however.