Honestly, I've never had problems with withdrawals; of course, I've also never won large sums, so I can't say for sure, but, as discussed in other threads, every story has two sides, and fraud can happen on both sides. In a way, when a casino, in its terms of use, states that it may request "additional documents" or proof of income or that it may refuse to pay if it suspects something, it's because it's already preparing to avoid future complaints in these cases.
So many people have complained of having problems for withdrawal in gambling platforms, i believe that why some people are having issues with withdrawal is because of they used fake documentation to verify their account or they refused to follow the rules and regulations of gambling platforms, I believe that is the major problem that can warrant a gambler not to have access to make a withdrawal when due in gambling...
Every casinos have their own jurisdiction about how to treat their users and when to enforce it. Sometimes casinos decisions about a certain situation may not be fair enough depending on who is involved and how they want the issue to be resolved.
There are casinos that even if you cheated on their platform, they will not close your account if you have been playing bets on their platform for long and you have been known to be a potential customer that had referred some other players to use the platform.
No business will want to lose their potential customers even if anything goes wrong. This is actually a business of continuous income generation.