Socio-psychologically speaking, these powers in the EU are suffering from what is called “Stockholm Syndrome”. It is as if they are in a condition that causes them to develop a psychological alliance with their captors- the Trump Administration- as a survival strategy during captivity. They are feeling sympathy to dance tango with the US, even if there is no rhyme or harmony in terms of their policies.
Accordingly, to keep the JCPOA alive, the leaders from France, UK and Germany are taking every steps, detaching themselves more and more from the concerns perceived by Iran and getting too much attached to addressing anxieties created- faked or not- by the new administration in the US.
Whilst, the EU leaders should come to this understanding that, in this formulation, there is a third party called Iran, and if Iran does not share the same feeling or suffer from the same syndrome, it, certainly, means that the final outcome would not be what they have expected and, their sympathy to their captors would mean the death of JCPOA.
Theoretically speaking, when a negotiation is concluded, the parties would not take a path to meet, separately afterwards, the points of controversies at the negotiation. Practically speaking, whatever it might be named – rectification, completion, addressing the flaws, etc. of the agreement, that would be in contradiction with the substance of the agreement and the context in which the agreement is reached. Additionally, according to JCPOA, best efforts will be made in good faith to sustain this agreement and to prevent interference with the realization of the full benefit by Iran of the sanctions lifting; therefore, any kind of dancing to the beat of the drum played by the US, even outside the JCPOA, would mean the actual non-compliance with the provisions of that treaty.
JCPOA was supposed to be considered as an agreement between 5+1 which gained an international status by the UNSC Resolution 2231. Naturally, any kind of changes in this agreement cannot be lead to sustainment and continuation of that agreement, unless it is done in a process with the participation of all 5+1 countries.