In version 6.9.2, Unraid added a lockout for 3 login attempts (per IP address). I often fail this and am locked out from the Web UI while I impatiently wait for the timeout to expire. Here is a quote from the release notes:
For webGUI login you now get 3 login attempts per IP address before a 15-minute cool off is enforced. Further, the timestamp of the last three failed login attempts per IP address are stored in files located in /var/log/pwfail/<ip-address>. Note this only applies to webGUI login, not ssh or telnet.
So, it appears that if you remove the file corresponding to your IP address on the Unraid server in the /var/log/pwfail directory, you don't have to wait for the timeout.