Probably the casino suspects that there may have been some violation of the rules or a game error. These things happen and if this is a game bug, the casino must consult that with game provider. This, unfortunately, always takes a long time. Unfortunately, such situations must always be carefully checked so that they do not happen again in the future.
This might not be a game bug because he is losing and winning like a normal bets of legit player. He just got lucky to win after the lose to be in that huge profit. I guess his account is subjected for investigation due to some connection with other account. Casino usually do that if a player win huge profit that is not usual to his previous profit records.
I think Duelbits are doing extra care on handling this case because 16,000$ still huge even if we assume that Duelbits has a huge bankroll. Remember that they are a business so every penny counts. I really just hope that they will speed up the investigation because I experienced same situation with OP for holding my account and it’s really frustrating if you can’t get an update even for a day.
Even there is alot players open VPN for slots and its allowed but me never ever touch it