1/ Some EU frustration at UK griping over trade problems and suggestions Brussels needs to improve its attitude to make the relationship work better. There's a feeling of déjà vu, that the UK never really accepted the practical reality of the deal it wanted and still doesn't.
2/ In particular there's exasperation that the UK is moaning about the deal not including arrangements that it ruled out itself to keep its own red lines intact. It's seen as a pattern of behaviour - first there was visa-free travel for musicians, now it's shellfish.
3/ EU sources say the lack of provisions on shellfish exports was brought up numerous times in the talks as a concern. But the UK refused to engage, as it did on wider SPS issues, over fears of 'being drawn into the EU's regulatory sphere'.
4/ The EU has rules vis-a-vis third countries, they say, and the UK knew this. Indeed, as they see things it's the British attitude that needs a reset. 'The problem is it wants to be a better third country than others, and that’s not an option.'
5/ That's seen as particularly rich after the UK turned down the EU's offer for a much closer relationship in pursuit of a 'Canada-style' one. Recent complaints perpetuate concerns the UK still hasn't really come to terms with the sovereignty/access trade-off.