I've been gambling a bit for years, but recently I've made some great earnings, so I wanted to withdraw, and my payout is pending. I saw that it has to be reviewed manually, so I did some research since I've never seen this message in the past, and I came across this thread and read all the recent complaints. Should I be worried?

There have been cases in which withdrawals were flagged to be reviewed manually.
As far as I know, they sometimes flag withdrawals to be reviewed manaully if they find them suspicious or there's the probability of the user abusing the website with bots or multiple accounts.