We decided to manually re-do the permissions instead of running the PowerShell script. We believe that its about time to audit and arrange the permissions as they were MESSY! Thank you for all your help. I've come across many issues in the past and most of your answers helped me a lot! so.... Thank you very much! :)

Hi Trevor, the content database has been attached successfully through Central Admin "Add content database" option to the new Web Application. However, I noticed that some of the permissions were lost and some were retained. Hope you can provide your insights regarding this. Thanks!

Thanks for the details Trevor. Will give an update tomorrow and hopefully it's a favourable result. Fingers crossed. :)

Hi Trevor, it will come from the same farm. No plans on running the Convert-SPWebApplication. In fact, the planned script would be Mount-SPContentDatabase "myDatabase" -DatabaseServer "myServer" -webapplication http://sitename **-NoB2bSiteUpgrade** and yes we'll do SQL backup too. Given this, I believe we won't be having any problem doing a rollback, yes?

Thanks Trevor! that did the trick!

Hi @GregW, I've checked the registry and it appears that loop back check is already disabled. (I didn't know at first because I became an interim administrator when my colleague left the company). I would probably request our security team to check for the white listed host names.