Just for the record, putative UK breaches of legal duties in relation to own Withdrawal Agreement so far include: 1) deliberately misrepresenting nature of UK obligations under NI Protocol = breach of Article 4(3) TEU + Articles 5 and 127 WA (esp as clarified by European Council)
2) unreasonably refusing EU request to operate premises in Belfast as required for effective implementation of UK obligations under NI Protocol = breach of Article 4(3) TEU + Article 5 WA read in the light of Article 12 IRL/NI Protocol
3) failing to notify EU of problems with "settled status" scheme, due to virus crisis, warranting automatic extension of deadline for applications = breach of Article 4(3) TEU + Article 5 WA read in light of Article 18(1)(c) WA. As far as I know: happy to be corrected if they did
Remember: ECJ remains primary dispute settlement body for all problems arising during transition period (arbitration panels only start after end of transition). Maybe Commission should be thinking: use time to start building up caselaw on what "good faith" means for UK Agreement?
ps, insofar as any EU27 has encountered similar problems registering UK nationals under Withdrawal Agreement: would also expect to notify & automatically extend applicable deadline. This facility doesn't depend on moral wrongdoing, just factual problems, so "virus crisis" counts.
To expand: European Council has it-and-reit-erated that duty of sincere cooperation is binding on UK & includes obligation to refrain from making public statements / claims that contradict letter or spirit of its own Withdrawal Agreement. EC's interpretation, but a compelling one
That "not actively undermining your own agreement" is a normal expectation under principle of sincere cooperation really shouldn't come as surprise. Except in Brexit Britain, where charlatans & liars are actively rewarded & their bad faith is celebrated as some princely virtue...
