then I found out that it was because I used different IP for each login and used it on different devices with different IPs. I haven't encountered this situation before, it seems like coinbase just changed their policy to be more strict to protect their users.
The tip when using coinbase is only to use 1 fixed IP, do not change too many IP, otherwise, they may continue to lock your account to ensure your safety.
Are you sure about this? Because modem assigning dynamic range of IP address are designed to used like that unless you configure to have it as static assigning which probably coinbase knows a lot about it. Unless a VPN, new device or new browser is used and it will trigger their system.
Though disabling the account looks like not normal to me for every suspicious login, except when changing email or password.