This has been reported by Preston and recently a new sandbox user had the similar issue. Here is email from the user:
"I created an account, create a new sandbox then realized I used the wrong email address. So I changed my email address now when I try to access the sandbox, it is suck in a loop. It goes from the https://sandbox.hspconsortium.org page to the https://sandbox.hspconsortium.org/after-auth page to the https://sandbox.hspconsortium.org/dashboard page back to the https://sandbox.hspconsortium.org and then it repeats. "
In the database it creates a new user without the smb_user_id and new email address.