Progress on the issue
I put in an implicit wait to the test, which give me some time to interact with the window.
After doing that, I found that if I open the developer tools panel, the selenium test proceeds as normal. The AWS form is populated with the expected
username and password, the login proceeds, the desired web page is pulled up and things go along correctly.
It narrows things down but doesn't answer what's happening.
Another workaround I found is that if I pass the "headless" option to the driver, the test proceeds as normal, though the chrome window is prevented from displaying.
I don't know if this will be sufficient as a workaround and still doesn't answer what's happening.
A friend suggested that newer versions of Chrome are disallowing interaction from untrusted sources. The selenium driver may be considered an untrusted source.
Once the developer panel is opened, chrome might be registering the interaction as from a trusted source (Windows OS and /or the current User) and then that's why
the test proceeds normally.