Felix actually doesn't have his Mercenary model unique, just Myrmidon (beginning class) and Swordmaster. Also, it seems like all the canon Priest/Bishops (Linhardt, Mercedes, Marianne) also use their unique models for the Monk beginning class.
It's something else than the time skip. Leonie's B support makes explicit reference to it, and therefore cannot be viewed until afterward. And you won't be able to accrue more support points until after you view the next support (in December).