Burp Suite "bad_certificate"?

Was just getting started on the Starting Point Unified challenge and am running into an issue where Burp Suite appears to be unable to capture the results of attempted logins.

“The client failed to negotiate a TLS connection to {IP}: Received fatal alert: bad_certificate”

I also noticed that the Unified machine seemed particularly slow to respond compared to others thus far. The nmap took forever. Shut down the machine and restarted with same results.

Looking for thoughts and suggestions on the Proxy sniff issue though mainly.

Well, I guess that is more of a warning than an error. Seems to work regardless but am still stuck at that point unable to capture what the walkthrough is guiding me toward.