SPSiteDataQuery does not return all results

Hi all,

I have created a visual web part to show all items with a specific Content Type using SPSiteDataQuery. It worked perfectly until I migrated data to my lists. Now my lists contain about 1000 items which all have same content type. I used PowerShell to migrate data to the lists. I tested during migration the web part showed the items when they were around 600 items but now after number of items come up to 900 it stopped retrieving all items. I have debugged SPSiteDataQuery retrieves only 9 results.

Any idea why SPSiteDataQuery does not retrieve all items? I appreciate all kind of advice.