I'm not going to call anyone out, but poor communication is at the top of my list, for example:
I sent scheduler email... Scheduler responds 5 minutes later (ok, great).... I respond 2 minutes later.... Scheduler then responds to that three days later. (This, in my opinion, demonstrates a lack of interest on the scheduler's interest to follow on the topic of the email, and thus poor communication).
Second example, I send email, and they respond, like they saw only two words of my message and not what I ws actually talking about.
There is one, who I am not going to mention, who I don't like mailing because it never goes smoothly. Others will respond but let's just say if they responded to you in that manner in a retail setting, they wouldn't good customer service scores. Most schedulers are not like this, and are great, so I am not going to mention those I don't like.
I will say this: I don't see "I have too many clients" as a reason to not communicate efficiently. I can't use "I have too many shops" to not end up doing one or two of them. I'm expected to take what I can handle and the workload that they present and I have the same expectations that schedulers do the same thing.