You shouldn't have issues with Nord VPN. Just don't forget to use it when logging in. The people I have heard that had problems were forgetting to log into VPN sometimes.
The issue boils down to Mutual Fund restrictions by these financial institutions.
Earlier this year Charles Schwab and Company, Fidelity Investment and T.Rowe Price announced that they would no longer allow Americans living overseas, even their own employees, to buy US based mutual funds.
The easiest thing is to use a USA mailing address and also have a utility bill under your name if possible. Previously they allowed you to send in two forms of proof including rental agreement, driver's license with that address, mortgage statement but some people are getting rejected with mortgage statements or rental agreements and they are wanting to see an actual utility bill. This is to cover that financial institution which may have severe penalties.