The user's passwords in POA and in PBA appear to be different (login to CCP is possible, but when switching to Account tab or using any billing-related link, an error occurs; it is not possible to login directly to Online store with the user's credentials). The "Forgot password?" link was used previously to change the password.
When resetting password via "Forgot password?" link on CCP login page, password on PBA side is not reset, the bug id is #POA-82789.
Update to POA 5.5.4, where the issue is fixed.
For user experienced an issue, synchronize the passwords by changing it from CCP/PCP.