Mixologist behind bar, but not tending it, unavailable for orders

It's really odd, sometimes they flip between being able to order or not in a matter of minutes. You can't really tell if they are just standing there or actually tending the bar as regular. I click on them several times and sometimes suddenly you can order. And a few minutes later you can't. They're then just hanging around chatting to other sims and doing whatever. But you can't tend the bar yourself or call a new host.  For a while there were no bar tenders at all and they 'fixed ' it sort half baked way and now there are sims there but they usually don't do anything.