Scenario Pattern so far from my run through this month:
Scenario:
13th Dec : 1 - 2 years - no visit
13th Dec : 2 - 4 years - no visit
16th Dec : 3 - 5 years - visit > Visit in Task List
16th Dec : 4 - 9 years - visit > Free Build
17th Dec : 5 - 5 years - no visit
24th Dec : 6 - 13 years - visit > Visit in Task List
24th Dec : 7 - 12 years - no visit
25th Dec : 8 - 11 years - visit > Visit in Task List
26th Dec : 9 - 21 years - visit > Visit in Task List
29th Dec : 10 - 49 years - no visit > Free Build
Apart from the Free Builds the inspector only comes when there is a task for it . so, I would deduce bug if an inspector visit is required and doesn't arrive otherwise deliberately turned off if not required and doesn't arrive. The only one that I am suspicious of is the difference between the Free Builds 4 and 10. One had visits and the other didn't. I think this may be just the case that they forgot to turn on the inspector. None of my regular zoos have a non visit unless the zoo is less than 2 years old so I would assume that Career Mode scenarios are turned off by default and turned on as needed and others are turned on by default and maybe turned off as needed. Once I have gone through the rest of the scenarios I will post up a bug/query report pointing out inconsistencies and theories and hopefully they will update the help explaining how the inspector/reporter works.