The concept of "reproducibility" is a hallmark of the scientific method, and so it is a common sub-argument against UAP studies: you cannot reproduce strange encounters; thus, you mustn't study them. That reasoning is fair when applied to psychics claiming to view the future, but not to UAP. We have just established that sightings occur in different countries. There are also "common shapes," implying reproducibility in descriptors. (Although the U.S. government thinks shapes should be classified! Why? (91)
Most damning of all: not all of the established sciences can rely on reproducibility in its most pure or direct form anyway! Take, for instance, cosmology — without access to the multiverse (if it even exists, of course), we have only 1 Universe or cosmos to study, with 1 Big Bang and 1 Cosmic Microwave Background (CMB). We can do computer simulations, of course, and come close to reproducing the conditions of the Big Bang in the highest-energy particle (LHC) or ion colliders (RHIC), but that's not the same as having multiple universes or many CMBs to study. Yet, cosmologists can still do their work.