In each level you can restart by pressing a key on your controller or keyboard but I don't know why, the level 50 seems different. If you die, You can only restart this level by clicking restart with your mouse.

This bug will only be a problem if you die on level 50 but still I reported it to the game devlopers on a steam forum here : https://steamcommunity.com/app/505210/discussions/0/2242175653296114093/

I hope this will be correct in a future but for now we need to deal with it.