Altium: Starved Thermal error
I don't know if this answers your question, but here area a few notes:

Your expansion and gap numbers are extremely tiny -- less than 4 mils. I'm not saying a board house can't do that, but you should consider making those larger or foregoing via reliefs. You might also consider modifying the relief conductor width. It is set to 0.5mm and is equal to your via size. This means that there is 100% coverage all the way around for conductors leading out of the via.... that is, it looks like a cross instead of four leads with arcs connecting them. This may be causing the conflict you're seeing when it tries to draw those.