Can anyone tell me the cause of this SLS imperfection?

Firstly id just like to say this part wasnt printed by Shapeways, so i havent added it in the 3d printing topic.
Id just like a second opinion.

The imperfection only appears on the same side of all the 10 prints.
There are small areas where there was no powder to begin with, or the laser hasn't hit it?

Is it possible to get bubbles during the process? over-heating the the material?

For reference, the part in the picture has a diameter of 10mm

That almost looks like they added some sprue during the printing process, and then snapped them off during cleaning.

Thanks for the reply.

They were printed within a box without sprue, so doubt this is the reason.

Some of them have a depth of just under 1mm

Thanks though.

If the imperfections were in the same place on all the print, it points to something on your meshes.

To me, it looks like unsinthered material which can be caused by the laser needing to be calibrated, or impurities in the material.

@ Bill , No the holes are in various places.

@Paul, thats what it looks like to me, they are reprinting them on a different machine to see if it reproduces the flaws.

Thanks for the replies.