In some cases, when creating your bracket, it gets unbalanced. It happens because the number of competitors in a brackets is always a power of two.
So if you have 20 competitors for example, it would round up to 32 competitors, which will give you 16 series of matches.
That’s due to the fact that it should balance to the next power of two in the next round (16)
So in the first round you should have 4 completed series (in which 4 competitors will be eliminated and 4 will reach the next round) and the other 12 competitors on a “bye” (standing alone in their series).
You should manually put those competitors who are on bye positions in the next round.
This will give you a balanced next round with 16 competitors in 8 completed series.
So, if you created a bracket stage with a number of competitors that is not a power of two (like the example above), some competitors will stay on “BYE” and you need to manually advance them to the next round.