What are possible reasons branch managers have given for not releasing a soldier from their current MOS to serve as an Army recruiter?

I recently submitted a voluteer recruiting packet and am worried that, if selected, my branch manager might not release me to the recruiting branch. Has anyone had any experience with this? What was the reason given for them not releasing you? Is there any way to fight this decision? Keep in mind I haven't been accepted yet. I have just had a difficult time with my branch manager in the past and am trying to be proactive in anticipating roadblocks.