You might see occasionally transparent donuts with a question mark in the centre. 

The transparent donuts are records for research outputs that do not yet have Altmetric Attention Scores (i.e., research outputs with no Altmetric mentions yet). The record was added to the Altmetric Explorer via a data implementation from an Altmetric Explorer for Institutions customer.

Transparent donuts might still have underlying attention data, such as Mendeley readers and Dimensions citations, but these data sources do not contribute to the Altmetric Attention Score. 

The donut will light up when it gets an Altmetric Attention Score in future. However, because a record of the research output exists in the Altmetric database, users can sign up for email alerts from the details page to monitor future attention.