Ways I've approached this and it hasn't been successful:
Using the same certificate as the SplunkWeb SSL certificate (splunkweb works on it's own with the SSL certificate being successful.)
Using a different certificate than the SplunkWeb SSL certificate (without a password)
Using a different certificate with a password, and configuring the server.conf to utilise that password
The moment that I configure the server.conf to not utilise the certificates I've created, splunkweb goes back to normal after I restart. And I can access the management port as well (even though the default certificates are invalid in the first place.)
Any ideas on what the problem might be, or if it's related to the current Splunk version?