Character slips when student hits play

My students are creating a platform game with Tynker.
They added 2 actors (hero and villain) from the level editor to their stage.
When they press play to see the game in action the actors SLIP from their original location without apparent reason.
I know that those actors already bring some ready made code…
Also the platform tiles my student created moves from up to down (it falls down).
I have turned off physics/gravity…
Does anyone know how can I correct this misbehaviour?
Thank you!