Problem started after upgrading from WinSCP 5.7.7 (Build 6257)
Transfer protocol = sFTP
When logging into WinSCP, there is a checkbox "Remember password for this session". Checking this box enables an automatic re-login when the current session expires.
After upgrading to WinSCP 5.9.1, the checkbox no longer does anything. And besides having to enter the password after every expired session, the initial login fails, you have to click the Reconnect button and enter the password for a second time before the login will complete. Issue also occurs with WinSCP 5.9.
As soon as I reverted back to WinSCP 5.7.7, the checkbox returned to working as expected.