Many reasons to trigger a platform tool to freeze/ block an account and it does not need to relate to compliance problems but also can be related to security issues.
If you don't break the platform's Terms of Service, you can submit documents or information to unfreeze your account. If a platform is legit, they will not permanently terminate your account because of VPN. If they do this, they should have more reasons for such serious termination.
If they have any doubts about us, they can ask us to do KYC, which has been a solution to eliminate the casino's doubts about its players. But if a violation occurs at the casino, the casino has the right to immediately block the gambler's account because they do not heed the rules that exist in the casino.
Legitimate gambling platforms will not find fault with their users but will provide good facilities but as users, we also have to follow the rules. And we also shouldn't find trouble with them by trying to break the rules.
They accept VPN and even allow users to change usernames but prevention is better than cure and if you can use their service without VPN, why do you need VPN and use it if you are aware that VPN can cause some kind of troubles in future?
That means users can safely use a VPN and there won't be any problems. But that will be up to each user because some users still want to use a VPN while others will not use a VPN to access their sites. It is about someone's comfort in visiting casino sites with or without a VPN.