ah, yes, that's more clear.
If you go just back and forth, the blue bar of progress remains the same.
If you train in the new version and go back to the old, the blue bar is reset ?
don't know, I just test it.
I had some progress in the old one, in the blue bar
went in the new version , did a train two twice, for a single player
then back to the old version but the gaining progress was the same (for the other players).
They didn't lost it. Maybe after the daily server maintenance ?