This may be unrelated but seems to have only appeared after I updated the Multisite Privacy plugin. If I go to a subsite and set a user's role to "No role for this site" the user disappears. The user still appears in the user count "all" but can't be accessed or edited. See the attached screenshot. Notice that it says there are 3 users but only 1 user is showing? The other two users were set to "No role for this site".