Did you rebuild your vb forum styles after making the changes for site url in admincp ? You don’t need baseurl config.php change really though. See https://www.vbulletin.com/forum/articles/4361080-converting-your-forum-to-https
Go to vBulletin Options > vBulletin Options > Site Name / URL / Contact Details.
Edit these three settings: ‘vBulletin URL’; ‘Login URL’; ‘Core URL’ and add the ‘s’ into the URL.
For example, if your URL is http://www.contoso.com/forum, change it to https://www.contoso.com/forum
NOTE: Do not remove the word ‘core’ at the end of the core URL. You will break your site!
Then go to Settings > Options > Server Settings & Optimization Options > Use Remote jQuery
Set this to Google.
The key to all three vBulletin versions is that all you do in the URL settings is change http to https. Do not alter any other part of the URL.
Once you have changed these settings, go to AdminCP > Maintenance > General Update Tools, and rebuild the styles. (In vB3 this is AdminCP > Maintenance > Update Counters). Leave the default settings and just run this update tool.