So it seems like White Fox's original plan of making Re:Zero season 3 being 38 episodes consists of Arc 5 and Arc 6 seems to be discarded. They will instead makes season 3 be 16 episodes only, and let the next 22 episodes (aka Arc 6) being labeled as season 4.
Reason why this became a thing was because of production issues behind White Fox studio. Good thing though, it seems like White Fox is putting more care for season 4 as Arc 6 is hailed as the greatest arc in all of Re:Zero. So I don't mind the wait.
Original source is from
Ice aka prominent leaker of Re:Zero.