Problem because it's not supported or problem due to fraud prevention by amex? I've travelled a lot and never had issues with amex or chase (once I used my chase credit card for the first time in over a year on the opposite side of the world and the transaction was instantly approved).

It depends on the bank, your profile, your visa/mastercard credit card type, the volume you are doing with the bank, etc…

Amex are less accepted because they have a higher processing fee.