It's unfeasible to carry out research on every little aspect of any medication, except for the very long term. That's why drugs get approved all the time, yet trials and studies continue for decades to account for long term and extremely rare side effects.
That said, literally anything can change the menstrual cycle (flu, stress, changes in nutrition or exercise levels), and especially given that menstrual symptoms correlate more with inflammatory markers than with actual hormone levels [0], it's to be expected that treatments that elicit an inflammatory response might have an effect in menstrual symptoms. It's good this research is done, but I doubt these changes come up as a surprise to any physician.
> Is it ethical to enforce vaccinations (via mandate) with these matters unresolved?
I think so, unless you consider to keep enforcing lockdowns, travel restrictions, or a Children-of-the-corn-light type of scenario to be ethically better.