This is one of the main reasons RocketJudge was created- the founders were sick of competitions being thrown into chaos if a few judges didn't show up. When you do assignments in advance, this can be especially challenging, as you have to redo assignments, potentially under a time crunch.
In our experience, about 20% of judges are no shows.
That's why RocketJudge doesn't assign judges until judges check in with a volunteer at a check in table or via self-check in.
That said, you still may have judges check in and then ignore their ballots. On the Judges tab, there's a column titled "Last Activity" where you get instant updates on a judge's most recent action. It might say "received email", "check in", or "last voted x seconds/minutes/hours ago." If they so much as sneeze, you know about it (a bit dramatic, but you get the idea).
Which is all to say, if a judge is not going to complete their ballot, you know about hopefully far enough in advance to do something about it (depending on how long your event is).
Generally, we recommend assigning additional judges to evaluate competitors that are assigned to no-show judges. Learn more about that here.