Why does the challenge s.36 have episodes 1-3 then jumps to episode 21 and nothing in between? Even though it is the current season
'Episode 21' is actually a preview episode, to be seen before episode 1, if you like that kind of thing. NOW TV have given it a confusing episode number when it doesn't actually have one.
As this show is currently being shown weekly on MTV in the UK you should expect a new episode each week.