As stated, multiple position training is slower, and if the players popped the previous week, then they are at a low sublevel, and will need more than one week worth of training to pop to a new level
Just because they don't pop, doesn't mean they didn't improve though. I had a trainee who didn't pop a level, but who changed his listed position, due to improvement of his sublevels. I believe, and see no reason or evidence to the contrary), that those higher sublevels are taken into account in the game engine calculations.