Yeah it's odd especially given the depth now in positions he can play.
Fullback: Bula, Attard, Bryenton, Nassar (Averillo as well)
5/8: Latu, Javon, Doeuihi, Averillo, Bryenton (possibly Schuster)
Lock: Twal, Mann, Brailey, Seyfarth, Sione, Lanyon, Murray, Havea Jr, Van Drie (possibly Doeuihi)
Hooker: Api, Brailey, Hayward, Lanyon, Havea Jr (even Mann can be thrown in there)
The only option I'd be ok with is if Mason is now physically trained & coached to be a Kurt Mann protege. High energy lock who can pinch hit at dummy half in short bursts & fill in as depth in the halves during a game if injuries strike.
No more fullback & cannot defend at centre.