I had the same issue: my accountant suddenly lost access to my QB and asked me to invite her again. I could not find any way to do it until I clicked on the gear button and in the very bottom of that window saw an option "switch to business view". There are 2 options: accountant view and business view. I was working in the accountant view. As soon as I switched to the business view, I was able to go to the Accountant feature and send an invitation by entering my accountant`s name and email address.

I hope this helps.