This is just a visual bug, as the intended moves are there if i click in the pokemon on the top left of the screen.
This bug happens when, prior to the level ups, i have free slots on the moves.
Yesterday i also saw that if i teach various moves in a row through level up, sometimes they don't appear in the next move, for example in the pic of that piplup if i teach peck in replace for bubble, the next move learned will show that bubble is still there instead of peck; but it is still just a visual bug.
I will try to use those procedures to see if it fixes the problem. Thank you for helping.