I am playing long war with no other game play effecting mods atm.
I have seen a couple of times now that when i trained sprinter from AWC that the 1 mobility bonus was not added to the mobility of the unit.
Edit I think the problem lies with the fact that the statusscreen isnt updated with the new stats.
I just had a shinobi train formidable and the statusscreen said That she had no armour, but when i took her on a mission the armour was there.
So maybe/probably the extra mobility was there aswell but with no information on the statusscreen there is no way for me to know.