Coinbase exchange was launched in 2012 right? Have there ever been any cases of users' assets being frozen and never released to them?
Mostly such kind of cases like freezing funds comes from Centralized exchange like coinbase which you had mentioned and many more. Mostly they freez fund of Thier customer on different bases like not providing KYC or submitting wrong information, some time payment of some illegal sites from your account and many more.
So the best option for everyone is to use decentralized exchanges which will provide you privacy and where you can feel safe.
But instead of centralized and decentralized exchanges you can you your hardware wallet where safety of your fund will be 100% sure.