For the sake of whatever type of protection we have concealed various strings of characters in that link as well as renamed the persons name to 'FirstName.LastName'
Error console reveals absolutely nothing.
Upon navigating back to the joomla side of the site as the page is blank and the only thing is that text in the address bar.. we can see that the user has not been logged in. Going now to whmcs.mydomain.com/ shows us there is a successful login to WHMCS.
Any word on this would be tremendous. Hopefully J!WHCS works with wildcard subdomains as we're too vested in the new subdomain dashboard naming.
Thanks for the question - it sounds like it may be K2 causing issues... if you have K2 installed in your Joomla environment, go to Joomla > Extensions > Plugin Manager then sort the list by the System type plugins and order it so you can rearrange the order of the plugins. Be sure the System - K2 plugin is the VERY FIRST plugin fired, THEN the System - JWHMCS plugin. If it is the other way around, there are issues with K2 and this is just one of the possible issues that can occur.