According to diplomats, the European Commission was so non-plussed by one of the UK's proposals in the legal text for the replacement backstop that they had to check whether it was a mistake by the Brits. It wasn't. (1)

It's over the UK's new Article 1⃣(a) for the Ireland protocol, which would commit both sides to no checks at the Irish border ever. This + possible Stormont veto - guarantees of what checks would happen in NI = big problem for the EU27 because it's a bit like a blank cheque. (2)

The UK also wants continued access to a number of EU databases for cross-border trade, even if Stormont were to reject the Irish border arrangements during the transition period. This was contained in a series of briefings for - and written up by - EU27 diplomats.(3)