Dbo:thumbnail - some URLs not working?

Data Data Quality
1 
@base <http://dbpedia.org/resource/> .
@prefix  dbo: <http://dbpedia.org/ontology/> .
@prefix  dbp: <http://dbpedia.org/property/> .
@prefix  dbr: <http://dbpedia.org/resource/> .

SELECT ?person ?thumbnail
WHERE
{
?person a dbo:Person;
        dbo:thumbnail ?thumbnail;
        dbp:name ?name.
FILTER(?person IN (<Robin_Ince>, <Brian_Cox_(physicist)>, <Richard_Dawkins>, <Mark_Gatiss>))
} LIMIT 10

RUN SPARQL above.

The SPARQL above returns basic info about 4 people - including a thumbnail image.
For some reason the returned data for Robin Ince doesn’t resolve the thumbnail URL.