There have been confusing letters from the CDF about this issue specifically. And the situation is so fluid that no real “factual” statement can be made about that. But again, where is this an issue? Nowhere.
A person can in fact, go to an SSPX Chapel for love of the EF, when no EF is available. And since both forms of Mass are valid, it does not make sense to say that it does not fulfill the obligation. If that were true the Vatican would have said that one does not fulfil the Sunday obligation at the SSPX, but they stopped short of that, in fact they even noted the difference about which sacraments do NOT fulfil obligations. (marriage and reconciliation)
In short, if I go to an SSPX confession, I did not fulfil my obligation to confess, I have not completed the sacrament. I should do it at a proper place. There is no requirement that if you have attended an SSPX Mass, you must then go to a regular Mass again on the same day if you have access to one.
So, it would seem that there are differences between obligations being fulfilled and not depending on the status, day, and availability of other avenues.
The situation with the SSPX is so volatile and fluid that I just do not see the value of this thread.