I do not consider bounties to be sometimes unpredictable because it has always been unpredictable not sometimes. Sometimes you may consider leaving a project for another with much hype and high rating on ico rating websites and later realized that the big mistake you ever did was leaving the project you were participating for another which sometimes may even end as a scam project. Do your research well and be ready to face the unpredictability of bounties.
That is why, Do with your own risk. Rating is not a guarantee that a bounty campaign will succeed, because many projects that have high ratings turn out to be a fraud. We also have to realize that there are a lot of risks as a bounty hunter, predictions that are not in line with expectations, choosing the wrong project, don't make us regret it. Choose a bounty with maximum analysis, even if that fails, consider risk.