The following is a message shared by Castle Learning regarding system slowness due to high volume of usage:

Thank you for your patience and understanding as we continue to work to implement changes to resolve slowness issues on our site that is impacting some of our users.  We are continuing to make tuning changes to the environment to support a significant increase in traffic and will be closely monitoring our systems.    We apologize for any issues this may have caused and hope to have services fully restored soon.