I was not able to log into my PayPal developer account until I delete the PayPal cookie from Chrome. This allowed me to log in, but by clicking "Profile" or "Settings" in the "Profile" drop-down list on the page with the message "Please log in to use the PayPal Sandbox features."
Logging in again did not help. Creating a new account (buyer or seller) also did not help.
This is in the new Sandbox environment.
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