All the $5 and $10 bundles I have been getting are mixed too, usually at least a couple runs of 15 or 20 in sequence though.
The teller probably had to wait for the safe timer to elapse to get at the bundles. The timer is for security if they are getting robbed, the robber has to wait 10 minutes to get at the loot.
So instead of good service I think she was slacking off because when I get my bundles the teller sets the safe timer then helps other customers. She uses an egg timer to let her know when the time has elapsed.