Yeah they have a very rough interpretation of what forward progress is. There is no rhyme or reason on when it's stopped it appears. Usually it benefits the offensive player they tend to give them the best spot when momentum is shifted from going forward to going in reverse. That's why can akers play could have been called off because his forward progress was halted and ball was not moving until he had been taken backwards.

On the other hand the ball carrier that picked up fumble advanced the ball forward out of the endzone and then retreated into the end zone and failed to advance the ball back out of the endzone. I saw safety but I guess you could argue his momentum carried him in the end zone before he established possession? To me he made a move to the endzone not sure if he was thinking touchback or trying to avoid a tackle.