Hi, I had the same issue and to fix it I applied the following solution:
Sometimes DB Connect won't run when minified mode is not enabled.
Minified mode describes the Splunk Enterprise mode wherein the static JavaScript files for modules are consolidated and minified. Minified mode is turned on by default using the minify_js attribute (set to True) in the web.conf file, and improves client-side performance by reducing the number of HTTP requests and the size of HTTP responses.
Setting minify_js to False turns off minified mode but DB Connect is not supported for this setting therefore you must use this:
minify_js = True
At the same time, I changed the default port from 9998 to 9085 but I do not thing this change is important to the solution, but I included it, just in case. I changed it because of the following documentation I found online (http://docs.splunk.com/Documentation/DBX/latest/DeployDBX/Troubleshooting):
Launching DB Connect results in a blank page
When you launch DB Connect, the RPC service attempts to bind to port 9998 by default. If port 9998 is already in use by another service, you will see a blank page.
To work around this, you can change the port number to which the RPC service binds. To do this:
Go to $SPLUNK_HOME/etc/apps/splunk_app_db_connect/local. If this local directory doesn't already exist, create it.
Open the inputs.conf file. If it doesn't already exist, create it.
Add the following stanza, if it doesn't already exist:
[rpcstart://default]
port = 9085
Restart Splunk Enterprise.
