MacBook Pro High Sierra changing Standard user to Admin not working
I stumbled upon what I think is the answer.

I recently purchased this MacBook as a refurbished unit. The administrator user was sold to me without a password for access purposes.

Once I set up a password, all of the admin operations began to function normally.

I don't have confirmation that this is a particular security feature for Admin users without a password set up, but it seems to have solved the problem.