Cannot login to admin area following initial setup

[scop]

Logging into the admin area at the end of the install wizard does not work for me. The login page just redirects back to itself. There are no errors in any logs or in the browser that I can see.

The credentials do actually work in other contexts, because when reissuing a license the installation prompts for those admin credentials, and accepts them there.

Same issue with WHMCS 8.1.0.1 and 8.1.1.2.

Followed instructions at https://docs.whmcs.com/troubleshooting/troubleshoot-authentication/login-redirect-loops/ (DisableSessionIPCheck, $session_handling = 'database') to no avail.