I can't comment on what's causing this - but I will say that it's gorgeous and appears to have had a lot of care in the layout and installation. Hope an expert can provide some insight.

Probably moisture wicking from the new mortar into the stone. If so it will probaby even out in a while. Can't say whether the chipping falls into the realm of "normal" for bluestone. Most old bluestone I see has plenty of chips, so I wouldn't particularly notice, but I don't know what the standard or expectation for new material is, I've only installed recycled.