Slipping chain

Hi. I have just installed a new cassette, new chain, new chainrings. All Shimano Tiagra. The indexing is working fine and the tension looks ok. Problem is the chain slips on sprockets 6 and 7 on the big and middle chainrings. It can't be wear because everything is new, and the hanger looks straight to my eye. I have two rear mechs and the same happens with both of them. Neither of these are new though.

Before I go off to LBS, does anyone have any suggestions please?