No, there are a lot of them actually. Instant withdrawals are one of the things that a gambler always requests so almost all casinos ensure that they have this. A delay, pending, and rejected payment can still happen though and that is to prevent an abuse. If there are newbies who came here to whine about this matter then we already know the reason why. But other than to prevent an abuse.
A problem in the blockchain can also be the reason like you said. I already tried playing on this casino here and so far I have had no problems. My withdrawals went smoothly and fast even though my first winning only came from their faucet.
I have also been around for a while now, and I don't have any withdrawals issues with most casinos most of them have instant withdrawal, unless those that allow users to adjust the transaction fees where sometimes the player lowers the fees themselves, this way the withdrawal may delay and like I said before all that is from blockchain and not the casino themselves since your transaction will be broadcast on the blockchain waiting for miners who will accept your fees before confirming your transactions.
*understanding all these techniques is a great way to effectively manage yourself around, no casino will withhold players' find unless there is a suspected case of abuse.