As of May is there still no fix, we did the same upgrade as well.  My employees are having issues and when I try to log in, after I put in my username and password it just sits there and does nothing.  I can't do anything with it.  Then I also get employees that try to log in and get an message that states "Your employer has adjusted your access to Workforce. You'll need to reach out to them to regain access."  Considering I can not adjust any access to this or even at this point get in to invite anyone......by the way I am the admin.  Anyone know anything to help.